This is not to deny that the Black gospel music of the early twentieth century differed in important ways from the slave spirituals. Whereas spirituals were created and dis- seminated in folk fashion， gospel music was composed，(5) published， copyrighted， and sold by professionals. Never- theless， improvisation remained central to gospel music. One has only to listen to the recorded repertoire of gospel songs to realize that Black gospel singers rarely sang a song precisely the same way twice and never according to(10)its exact musical notation. They performed what jazz musi- cians call "head arrangements" proceeding from their own feelings and from the way "the spirit" moved them at the time. This improvisatory element was reflected in the man- ner in which gospel music was published. Black gospel(15)composers scored the music intended for White singing groups fully， indicating the various vocal parts and the accompaniment， but the music produced for Black singers included only a vocal line and piano accompaniment.
17.Which of the following best describes "head arrange- ment" as the term is used in line 11?
(A) A published version of a gospel song produced for use by Black singers
(B) A gospel song based on a slave spiritual
(C) A musical score shared by a gospel singer and a jazz musician
(D) An informally written composition intended for use by a gospel singer
(E) An improvised performance inspired by the singer‘s emotions
18.The author mentions "folk fashion" (line 4) most likely in order to
(A) counter an assertion about the role of improvi- sation in music created by Black people
(B) compare early gospel music with gospel music written later in the twentieth century
(C) make a distinction between gospel music and slave spirituals
(D) introduce a discussion about the dissemination of slave spirituals
(E) describe a similarity between gospel music and slave spirituals
19.The passage suggests which of the following about Black gospel music and slave spirituals?
(A) Both became widely known in the early twentieth century.
(B) Both had an important improvisatory element.
(C) Both were frequently performed by jazz musicians.
(D) Both were published with only a vocal line and piano accompaniment.
(E) Both were disseminated chiefly by Black singing groups.
20.Of the following sentences， which is most likely to have immediately preceded the passage?
(A) Few composers of gospel music drew on traditions such as the spiritual in creating their songs.
(B) Spirituals and Black gospel music were derived from the same musical tradition.
(C) The creation and singing of spirituals， practiced by Black Americans before the Civil War， continued after the war.
(D) Spirituals and gospel music can be clearly distinguished from one another.
(E) Improvisation was one of the primary charac- teristics of the gospel music created by Black musicians.
About a century ago， the Swedish physical scientist Arrhenius proposed a law of classical chemistry that relates chemical reaction rate to temperature. According to the Arrhenius equation， chemical reaction are increasingly(5) unlikely to occur as temperatures approach absolute zero，and at absolute zero (zero degrees Kelvin， or minus 273 degrees Celsius) reactions stop. However， recent experi- mental evidence reveals that although the Arrhenius equa- tion is generally accurate in describing the kind of chemical(10)reaction that occurs at relatively high temperatures， at tem- peratures closer to zero a quantum- mechanical effect known as tunneling comes into play; this effect accounts for chem- ical reactions that are forbidden by the principles of classi- cal chemistry. Specifically， entire molecules can "tunnel"(15)through the barriers of repulsive forces from other mole- cules and chemically react even though these molecules do not have sufficient energy， according to classical chemistry，to overcome the repulsive barrier. The rate of any chemical reaction， regardless of the tem-(20)perature at which it takes place， usually depends on a very important characteristic known as its activation energy. Any molecule can be imagined to reside at the bottom of a so- called potential well of energy. A chemical reaction corre- sponds to the transition of a molecule from the bottom of(25)one potential well to the bottom of another. In classical chemistry， such a transition can be accomplished only by going over the potential barrier between the wells， the height of which remains constant and is called the activa- tion energy of the reaction. In tunneling， the reacting mole-(30)cules tunnel from the bottom of one to the bottom of another well without having to rise over the barrier between the two wells. Recently researchers have developed the concept of tunneling temperature： the temperature below which tunneling transitions greatly outnumber Arrhenius transi-(35)tions， and classical mechanics gives way to its quantum counterpart. This tunneling phenomenon at very low temperatures suggested my hypothesis about a cold prehistory of life：the formation of rather complex organic molecules in the(40)deep cold of outer space， where temperatures usually reach only a few degrees Kelvin. Cosmic rays (high-energy pro- tons and other particles) might trigger the synthesis of simple molecules， such as interstellar formaldehyde， in dark clouds of interstellar dust. Afterward complex organic(45)molecules would be formed， slowly but surely， by means of tunneling. After I offered my hypothesis， Hoyle and Wickramasinghe argued that molecules of interstellar form- aldehyde have indeed evolved into stable polysaccharides such as cellulose and starch. Their conclusions， although(50)strongly disputed， have generated excitement among inves- tigators such as myself who are proposing that the galactic clouds are the places where the prebiological evolution of compounds necessary to life occurred.
21.The author of the passage is primarily concerned with
(A) describing how the principles of classical chem- istry were developed
(B) initiating a debate about the kinds of chemical reactions required for the development of life
(C) explaining how current research in chemistry may be related to broader biological concerns
(D) reconciling opposing theories about chemical reac- tions
(E) clarifying inherent ambiguities in the laws of clas- sical chemistry
22.According to the passage， classical chemical reactions and tunneling reactions are alike in which of the fol- lowing ways?
(A) In both types of reactions， reacting molecules have to rise over the barrier between the two wells.
(B) In both types of reactions， a transition is made from the bottom of one potential well to the bottom of another.
(C) In neither type of reaction does the height of the barrier between the wells remain constant.
(D) In neither type of reaction does the rate of a chemical reaction depend on its activation energy.
(E) In both types of reactions， reacting molecules are able to go through the barrier between the two wells.
23. According to the Arrhenius equation as discussed in the passage， which of the following statements about chemical reactions is true?
(A) Chemical reactions are less likely to occur at tem- peratures close to absolute zero.
(B) In some cases the rate of a chemical reaction is related to temperature and in other cases it is not.
(C) Chemical reactions frequently occur at a few degrees above absolute zero， but they are very unpredictable.
(D) The rate of a chemical reaction depends on many other factors besides temperature.
(E) Chemical reaction rate and temperature are not related.
24.The author‘s attitude toward the theory of a cold pre- history of life can best be described as
(A) neutral
(B) skeptical
(C) mildly positive
(D) very supportive
(E) pointedly critical
