1.    (B). When something “alters,” it “changes” or takes a different form. See Exercises R1-R3.

2.    (A) The passage states that the rate of decay is constant, regardless of conditions. See Exercises R9-R14.

3.    (B) The element’s half-life is the time necessary for one-half of the original number of radioactive atoms in a sample to decay. See Exercises R4-R8.

4.    (B) The rate at which a radioactive element decays, its half-life, is used as a way to calculate its age. Sec Exercises R9-R14.

5.    (B! According to the passage, “Rocks as old as 4.6 billion years can be dated with some degree of reliability.” This implies that dating rocks that are older than this is probably less reliable. See Exercises R15-R21.

6.    (A) The phrase “from this point” refers to the separation of rubidium and strontium that occurs when the minerals crystallize from magma or metamorphic rock. That point is when the elements are incorporated into the minerals. See Exercises R4-R8.

7.    (D) When something is “essential,” it is “vital” or necessary. See Exercises R1-R3.

8.    (C) According to the passage, when an organism dies, “no more carbon dioxide is absorbed.” See Exercises R9-R14.

9.    (A) According to the passage, the nitrogen-14 isotope leaks out so it cannot be used for comparisons. See Exercises R9-R14.

10.    (D) The passage states that the amount of carbon-14 in the dead organism becomes less over time. Sec Exercises R9-R14.

11.    [C] The information about the kinds of isotopes taken in from the atmosphere would follow the fact that the isotopes are in the same amount in the atmosphere as in the organism. It would precede the information about what happens after an organism dies. See exercises R4-R8.

12.    Rubidium-87

(D)    Rubidium-87 has a half-life of nearly 48.8 billion years.

(E)    Rubidium-87 is incorporated into minerals as they crystallize from magma or metamorphic rock. (I) Rubidium-87 is formed when the rock is formed. Carbon-14

(A) Bones or wood are organic materials.

(C) Carbon-14 is an essential element of the cells being incorporated into living tissue.

|F) Carbon-14 has the progeny nitrogen-14, which is a gas that leaks out of the organism and, therefore, is not useful for dating.

(H) Trees are organic.

See Exercises R22-R24.

13.    (D) The number of births is divided by the total population. See Exercises R4-R8.

14.    (A) Demographers use the model because it helps to explain changes in population. See Exercises R9-R14.

15.    (B) When something is “portrayed,” it is shown or “represented” in a visual or verbal form. See Exercises R1-R3.

16.    (D) There is no information given as to the number of women who died while giving birth. See Exercises R9-R14.

17.    (B) The fluctuations in total population due to epidemics indicate a drop followed by a rise. There was a gradual rise overall. See Exercises R15-R21.

18.    (C) “Agrarian” occupations refer to those that are agricultural, in other words, occupations dealing with “farming.” See Exercises R1-R3.

19.    (C) The increased urbanization reduced the incentive to have a large number of children. See Exercises R9-R14.

20.    (A) The birth rate may fall below the death rate (deaths exceed births) and without immigration (there is no immigration) the total population may slowly decrease (the population gradually declines). See Exercises R9-R14.

21.    (B) Something that is at an “equilibrium” level is at a “stable” level or is balanced. See Exercises R1-R3.

22.    (A) The improvements in health have caused an imbalance of births over deaths. See Exercises R9-R14.

23.    (A) The earlier “pessimistic” predictions were that the population explosion would continue were based on the length of time the demographic transition took place in Europe (200 years). However, the transition in less developed countries seems to be occurring faster than predicted. See Exercises R15-R21.

24.    (A) The information about why in cities there was less incentive for large numbers of children would follow the statement that industrialization had led to urbanization. See Exercises R4-R8.

25.    (B), (C), and (E) In the preindustrial era, there were high birth and death rates with only a gradual population increase. This was followed by dramatic increases in population as improved health caused a decline in the death rate. Economic pressures reduced the birth rate, bringing the population to zero growth. See Exercises R22-R24.

26.    (A) When something is put into an underground “chamber,” it is put into a large “cavity” or hole that forms a roomy area. See Exercises R1-R3.

27.    (B) The commission understood that the waste may be hazardous for people thousands of years in the future and that these future generations need to be warned of the danger. Sec Exercises R4-R8.

28.    (D) The author mentions different circumstances to help the reader understand that even though we

think that future societies may be sophisticated, they may not be, and therefore we cannot leave the matter to chance. See Exercises R15-R21.

29.    (C) A “scourge” is a source of extensive “affliction” and devastation. See Exercises R1-R3.

30.    (A) The message must be understandable to any person no matter what his or her cultural background or knowledge is. See Exercises R9-RI4.

31.    (B) The author mentions the second law of thermodynamics to explain why materials can’t endure. See Exercises R15-R21.

32.    (C) The word “its” refers to the committee formed to guard a certain kind of knowledge. See Exercises R4-R8.

33.    (D) The committee that guards and passes on specialized knowledge has been called an “atomic priesthood” because it is rather like a priesthood in its exclusiveness and its monopoly of knowledge about nuclear waste sites. See Exercises R15-R21.

34.    (D) A “sanction” is a “penalty” used to obtain conformity to someone’s wishes. People who do not observe sanctions are punished through legal or moral pressure. See Exercises R1-R3.

35.    (A) The idea of a relay system is to pass on information over just a few generations. This would help to prevent the breakdown of communication over long periods of time. See Exercises R9-R14.

36.    (A) The author points out that those who have exclusive knowledge could use it to control those who are ignorant. See Exercises R9-R14.

37.    (D) While the exclusiveness of the atomic priesthood might lead to other problems, it is not mentioned as a difficulty in devising a communication system with the future. Rather, it is the main proposal put forward for making that communication possible. See Exercises R9-R14.

38.    [B] Finding efficient ways to deactivate nuclear waste materials is an example of a technological advance that could be made to solve this problem. See Exercises R4—R8.

39.    (A), (D), and (F) All of the various means of storing and passing on information pose a problem in communicating with the future because of the physical decay of storage media. A relay system could be used in which the knowledge is passed by a selected group of people. However, the proposal has potential problems of creating a divided society. See Exercises R22-R24.