摘要： 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 答案 B 解析 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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