题目内容
The country has already sent up three unmanned spacecraft,the most recent at the end of last March.?
A.has been launched B.having been launched?
C.being launched D.to be launched
B
句中没有连接词,故不能选作谓语动词的A项;the most recent having been launched为独立主格结构,由at the end of last March可知应选用表示动作完成的B项。
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