单项选择题

Human beings are animals. We breathe, eat and digest, and reproduce the same life (21) common to all animals. In a biological laboratory rats, monkeys, and humans seem very much the same.
However, biological understanding is not enough: (22) itself, it can never tell us what human beings are. (23) to our physical equipment the naked human body—we are not an (24) animal. We are tropical creatures, (25) hairless and sensitive to cold. We are not fast and have neither claws nor sharp teeth to defend ourselves. We need a lot of food but have almost no physical equipment to help us get it. In the purely physical (26) , our species seems a poor (27) for survival.
But we have survived—survived and multiplied and (28) the earth. Some day we will have a (29) living on the moon, a place with neither air nor water and with temperatures that turn gases into solids. How can we have done all these things Part of the answer is physical. (30) its limitations, our physical equipment has some important (31) . We have excellent vision and hands that can (32) objects with a precision unmatched by any other (33) . Most importantly, we have a large brain with an almost (34) number of neural (35) 。