青蛙是一种两栖动物，它的生殖方式是[ ]
A．卵生，体内受精
B．卵生，体外受精
C．胎生，体内受精
D．胎生，体外受精
答案：B
Last year I was often ill, but now I am good health.
A．at
B．of
C．in
D．under
胎儿肺成熟度L/S比值应是（）.
A.>1/2
B.>1
C.>1.5
D.≥2
E.≥3
