Oscar and Jack are identical twins, separated when they were babies by their parent's divorce.  Jack was brought up by their Jewish father in Trinidad, Oscar went to live with their mother's family in Czechoslovakia. In fact Oscar did not know he was Jewish until Jack found him in Germany in 1954. Jack is proud to be a Jew, but Oscar still does not like to talk about his Jewish heritage. Yet the twins are similar in many ways. They both like spicy food and sweet drinks.  In school they both did well in sports but poorly in mathematics.
　　Are thoughts and behavior determined by heredity (遗传) or by environment? Social scientists have long been interested in this question; the results of "twin studies" are particularly interesting to them. Twin studies of the similarities and differences between twins. There are two types of twins: identical twins, who look exactly the same because they have identical genetic characteristics, and fraternal twins, who have different genetic characteristics. In a 1937 study, Newman, Freeman, and Halzinger found that identical twins are more similar in height and weight than fraternal twins. Because identical twins have the same genetic characteristics, the conclusion was that size is determined more by heredity than by environment. In 1962, James Shields compared the height, weight, and intelligence of identical twins who were brought up together (in the same environment) with those of identical twins brought up apart (in different environments). He found that although the differences were small, identical twins who were brought up together were more similar than those brought up apart. Shields concluded that height, weight, and intelligence are largely determined by heredity. However, because of the differences between identical twins brought up together and those brought up apart, these characteristics may be partly determined by environment.
　　In the case of Oscar and Jack, heredity seems to determine physical and mental abilities, tastes, and behavior. Environment seems to determine thought.

　　21.   After their parents' divorce, Oscar and Jack ______.
　　A.   went to live with their mother's family
　　B.   were brought up by their father
　　C.   never saw each other again
　　D.   were separated until 1954

　　22.   Although Oscar and Jack are similar in many ways,  they seem to be different in
　　A. physical ability                                       B.  behavior
　　C. mental ability                                          D.  thought

　　23.  Identical twins are more similar than fraternal twins because
 　　A. they have the same mother
　　B.   they have the same genetic characteristics
　　C.   they were brought up together
　　D.   they were born at the same time

　　24.    The conclusion of Newman,  Freeman and Halzinger's 1937 twin study was that
　　A.   size is determined by height, weight, and environment
　　B.   identical twins are taller and heavier than fraternal twins
　　C.   size is determined more by heredity than by environment
　　D.   identical twins are more similar than fraternal twins

　　25.   Shield drew a slightly different conclusion from his study because_______.
　　A.   he also compared the intelligence of the twins in his study
　　B.   he compared twins brought up together with those brought up apart
　　C.   only identical twins were included in his study
　　D.   all of the environment factors were carefully controlled

　　答案：21. D   22. D   23. B   24. C   25. B