在人体的生殖过程中，精子和卵细胞的结合的过程叫[ ]
A．分娩
B．怀孕
C．排卵
D．受精
答案：D
_______, I think, and all the problems could be settled.
A．If you make more efforts
B．Making more efforts
C．A bit more effort
D．To have made more efforts
我国大部分地区位于（ ）
A．热带气候
B．寒带气候
C．温带气候
D．苔原气候
