Directions: In this part , there is a passage with ten blanks . For each blank there are four choices marked A , B , C and D . Choose the best answer for each blank and mark your answer on the ANSWER SHEET .

　　In the past few decades , remarkable findings have been made in ethnology , the study of animal social behavior . Earlier scientists had 1 that nonhuman social life was almost totally instinctive or fixed by genetics . Much more careful observation has shown that 2 variation occurs among the social ties of most species , showing that learning is a part of social life . That is , the statuses are not solely fixed by the genes 3 ，the learning that occurs is often at an early age in a process that is called imprinting . Imprinting is clearly not instinctive , but it is not quite like the learning of humans ; it is something in between the two . An illustration best 4 the nature of imprinting .Once, biologists thought that ducklings followed the mother duck because of instincts . Now we know that , shortly after they hatch , ducklings fix 5 any object about the size of a duck and will henceforth follow it . so ducklings may follow a basketball or a briefcase if these are 6 for the mother duck at the time when imprinting occurs . Thus , social ties can beconsiderably 7 , even ones that have a considerable base 8 by genetics .

　　Even among the social insects something like imprinting must influence social behavior . For example , biologists once thought bees communicated with others purely 9 instinct . But , in examininga " dance”that bees do to indicate the distance and direction ofa pollen source , observers found that bees raised in isolation could not communicate effectively . At a higher level , the genetic base seems to be much more for an all-purpos learning rather than the more specific responses of imprinting . Chimpanzees , for instance , generally 10 very good mother but Jane Goodall reports that some chimps carry the infant upside down or otherwise fail to nurture the young .

　　1. A. assumed B. adopted C.believed D. surmised

　　2. A. considerate B. considerated C. considerable D. considering

　　3. A. What’s more B. Hence C. But D. However

　　4. A. clarifies B. classifies C. defines D. outlines

　　5. A. on B. with C. in D. within

　　6. A. appropriated B. substituted C. assigned D. distributed

　　7. A. varied B. deviated C. differed D. altered

　　8. A. fashioned B. modified C. influenced D. affected

　　9. A. by B. out of C. from D. through

　　10. A. prove B.make C. turn D. create