My pen pal often helps me _________ my English. [ ]
A. in
B. at
C. about
D. with
答案:D
染色体是由_________和_________组成的。
风湿性心脏病二尖瓣狭窄时,心影呈()
A.梨形心
B.横位心
C.靴形心
D.悬滴状心
E.球形心