问题
It still puzzles the science world why some mammals produce their young ______ and hatching while others _____ to young babies.[ ]
A: lying eggs; giving birth
B: by laying eggs; by giving birth
C: by laying eggs; give birth
D: laying eggs; giving birth
B: by laying eggs; by giving birth
C: by laying eggs; give birth
D: laying eggs; giving birth
正确答案是：
