What does 'fill in the blanks' in the first paragraph mean?
A.To do the exercisE.
B.To take the test.
C.To know the right words.
D.To know the answer.

A.To
B.
B.To
C.
C.To
D.
D.To

【参考答案】

D
解析：短语fill in the blanks的意思是“填空”。短文一开始就提出一个问题：鸟类在长途迁徙的过......

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