You needn’t have come in person --- a letter _____enough.  [ ]

A. would be      

B. is      

C. would have been      

D. was

高血压是遗传易感性和环境因素相互作用的结果，一般认为遗传因素所占的比例是（）

A.60％

B.40％

C.50％

D.20％

E.30％