2. 外语
  3. Dung beetles ______ an integral part of the successful management of diary farms in Australia over the past few decades.

Dung beetles ______ an integral part of the successful management of diary farms in Australia over the past few decades.

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问题 Dung beetles ______ an integral part of the successful management of diary farms in Australia over the past few decades.
选项 A、has become
B、have become
C、became
D、had become
答案B
解析 时态题。在由until(till，up to)now，up to the present，so far，in (for，over，during)the past(last，recent)few(several，two．．．)months(days．．．)等构成的短语作状语的句子中常用现在完成时。主语dung beetles复数形式，故B正确。
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