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(A) The huge dust clo8ud described in the passage would have blocked the transmission of sunlight and lowered the earth's temperature.
(B) A layer of sedimentary rock takes millions of years to harden.
(C) Layers of sedimentary rock are used to determine the dates of prehistoric events whether or not they contain iridium.
(D) Sixty million years ago there was a surge in volcanic activity in which the matter spewed from the volcanoes formed huge iridium-rich dust clouds.
(E) The iridium deposit occurred at about the same time that many animal species became extinct and some scientists have theorized that mass dinosaur extinctions were caused by a meteorite collision.
18. Mary, a veterinary student, has been assigned an experiment in mammalian physiology that would require her to take a healthy, anesthetized dog and subject it to a drastic blood loss in order to observe the physiological consequences of shock. The dog would neither regain consciousness nor survive the experiment. Mary decides not to do this assignment.
Mary's decision most closely accords with which one of the following principles?
(A) All other things being equal, gratuitously causing any animal to suffer pain is unjustified.
(B) Taking the life of an animal is not justifiable unless doing so would immediately assist in saving several animal lives or in protecting the health of a person.
(C) The only sufficient justification for experimenting on animals is that future animal suffering is thereby prevented.
(D) Practicing veterinarians have a professional obligation to strive to prevent the unnecessary death of an animal except in cases of severely ill or injured animals whose prospects for recovery are dim.
(E) No one is ever justified in acting with the sole intention of causing the death of a living thing, be it animal or human.
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