习惯性流产的定义是指自然流产连续发生几次或以上()
A.6次
B.5次
C.4次
D.3次
E.2次
参考答案:D
解析:习惯性流产指自然流产连续发生3次或3次以上者。
It is thirty years since my father ______ in love with oil painting so that he is a famous painter now. [ ]
A. was
B. fell
C. enjoyed
D. loved
种群的年龄结构包括()
A、增长型
B、稳定型
C、衰变型
D、变迁型
E、跃衰型