1.(Z)The Earth’s rivers constantly carry dissolved salts into its oceans. Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth’s oceans can be accurately estimated.
Which of the following is an assumption on which the argument depends?
A. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
B. At any given time, all the Earth’s rivers have about the same salt levels.
C. There are salts that leach into the Earth’s oceans directly from the ocean floor.
D. There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
E. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
2.(Z)Most household appliances use electricity only when in use. Many microwave ovens, however, have built-in clocks and so use some electricity even when they are not in use. The clocks each consume about 45 kilowatt-hours per year. Therefore, house holds whose microwave oven has no built-in clock use 45 kilowatt-hours per year less, on average, than do comparable households shoes microwave oven is other-
wise similar but has a built-in clock.
Which of the following is an assumption on which the argument depends?
A. Households that do not have a microwave oven use less energy per year, on average, than do households that have a microwave oven.
B. Microwave ovens with a built-in clock do not generally cost more to buy than microwave ovens without a built-in clock.
C. All households that have a microwave oven also have either a gas oven or a Conventional electric oven.
D. Households whose microwave oven does not have a built-in clock are no more likely to have a separate electric clock plugged in than households whose microwave oven has one.
E. There are more households that have a microwave oven with a built-in clock than there are households that have a microwave oven without a built-in clock.
3(Z). The milk of many mammals contains cannabinoids, substances that are known to stimulate certain receptors in the brain. To investigate the function of cannabinoids, researchers injected newborn mice with a chemical that is known to block cannabinoides from reaching their receptors in the brain. The injected mice showed far less interest in feeding than normal newborn mice do. Therefore, cannabinoids probably function to stimulate the appetite.
Which of the following is an assumption on which the argument depends?
A. Newborn mice do not normally ingest any substance other than their
mothers’ milk.
B. Cannabinoids are the only substances in mammals’ milk that stimulate the appetite.
C. The mothers of newborn mice do not normally make any effort to encourage their babies to feed.
D. The milk of mammals would be less nutritious if it did not contain cannabinoids.
E. The chemical that blocks cannabinoids from stimulating their brain receptors does not independently inhibit the appetite.
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