In recent years a number of communication satellites ______ into orbit about the earth.A.

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In recent years, a number of communication satellites ______ into orbit about the earth.

A.have been put

B.has been put

C.are already put

D.have been putting

请帮忙给出正确答案和分析,谢谢!

热搜:所有者权益包括A实收资本B股本C