题目内容
9. It still puzzles the science world why some mammals produce their young by________ (lay) eggs and hatching while others by______ (give) birth to young babies.
9. laying;giving
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题目内容
9. It still puzzles the science world why some mammals produce their young by________ (lay) eggs and hatching while others by______ (give) birth to young babies.
9. laying;giving