Dung beetles ______ an integral part of the successful management of diary farms in Austra
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Dung beetles ______ an integral part of the successful management of diary farms in Australia over the past few decades.
A．has become
B．have become
C．became
D．had become
请帮忙给出正确答案和分析，谢谢！
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正确答案：B
时态题。在由until(till，upto)now，uptothepresent，sofar，in(for，over，during)thepast(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dungbeetles复数形式，故B正确。