单项选择题

Two competitors battle each other in each match of a tournament with nine participants. What is the minimum number of matches that must occur for every competitor to battle every other competitor（）

A. 27
B. 36
C. 45
D. 64
E. 81

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问答题

Select the sentence within the passage that illustrates a possible minimum level of sleep necessary for full functionality in the animal world.

单项选择题

A baby polar bear named Knut at the Berlin Zoo is the epicenter of a debate about animal rights and the ethics of keeping animals in captivity. Knut and his brother were abandoned by their mother after being born at the zoo. Knut’s sibling died, and Knut himself would have died as well, had the zoo officials not intervened. The zoo workers have been bottle-feeding the bear, and providing it with nourishment and care. Yet certain animal-rights activists say that the bear would have been better off dead than raised by humans, and some go as far as to say that Knut should be killed. They believe that the current treatment of the bear is inhumane, and will lead to future difficulty for Knut in interacting with other polar bears. They argue that since the mother rejected the cub, the zoo workers should have abided by the laws of nature, and the cub should have been allowed to die. Others have argued that in light of the fact that polar bears are an endangered species, it makes sense to keep as many bears as possible alive in captivity so that they can breed. The author mentions animal-rights activists in order to （）

A. explain how Knut became an orphan
B. exonerate the zoo workers
C. depict Knut's caretakers as unprofessional
D. foster the impression that polar bear's cannot exist in the wild
E. point out a counterargument to the zoo's position