摘要： 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

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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

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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

 

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