【单选题】

Few scientific fields are as full of risk as that of research into human intelligence. The two questions that (1) over and over again are "is it a result of nature or nurture " and "does race make a difference "

Making (2) comments about the second question can be a (3) move, as James Watson, a co-discoverer ofDNA、structure, recently founD、He suggested that he was " (4) about the prospect ofAfrica" (5) "all our social policies are based on the fact that their intelligence is the same as ours (white people) (6) all the testing says not really". Such (7) byDr. Watson are not merely (8) , they are scientifically weirD、If the term (9) has any useful scientific meaning, thenAfrica, the continent where modern humanity began, is most racially diverse. The resulting (10) among the public forcedDr. Watson to leave his laboratory.
(11) , the study of the first question (12) between intelligence and genetics— has some wiser practitioners. One of them, Terrie Moffitt, of King’sCollege, has just (13) a project judging the relative importance of nature and nurture.Dr. Moffitt’s team (14) the effect on intelligence of breastfeeding, but in a genetic context. Previous studies have shown that breastfed children are more intelligent, (15) about six IQ points, than those given baby formulas.
The team, however, (16) the involvement of a gene called FADS2, which comes in two varieties, known asC、and G. The researchers (17) if these two varieties interacted differently with breast milk. (18) on data from two groups of people, they found that the intelligence increase associated with breastfeeding only happened to people having (19) at least one copy of theC、variety. The effect did not. (20) on the social classes or IQs of the parents.
A．therefore
B．because
C．so
D．but