Question

()because only one baby panda is born to a mother each year

()because only one baby panda is born to a mother each year,giant pandas are becoming rare in the world

a probably
b the reason
c it might been
说说别的不是的原因

Answer 1

答案：A
解析：the reason一般不和because连用的；C的形式不对，might是情态动词，后面应该用动词原形，不能用过去分词。

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Answer 2

A.probably
前部分应该是一个从句,后面是主句giant panda...
如果选B,或C都无法构成主从关系或并列关系,因为之间没有并列连词and,but,or等连接..