18.The author mentions "folk fashion" (line 4) most likely in order to
(A) counter an assertion about the role of improvisation 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 characteristics 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 experimental evidence reveals that although the Arrhenius equation is generally accurate in describing the kind of chemical (10)reaction that occurs at relatively high temperatures, at temperatures closer to zero a quantum- mechanical effect known as tunneling comes into play; this effect accounts for chemical reactions that are forbidden by the principles of classical chemistry. Specifically, entire molecules can "tunnel" (15)through the barriers of repulsive forces from other molecules 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 socalled potential well of energy. A chemical reaction corresponds to the transition of a molecule from the bottom of (25)one potential well to the bottom of nother. 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 activation 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 protons 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 formaldehyde have indeed evolved into stable polysaccharides such as cellulose and starch. Their conclusions, although (50)strongly disputed, have generated excitement among investigators 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 chemistry were developed
(B) initiating a debate about the kinds of chemical reactions required for the development of life
(C) explaining how current research i