题目内容：

〖07山东〗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

优质解答

既然是last March,排除CD,因为是已经完成的
如果是A,就成了两个独立的句子,逗号不能连接两个独立的句子.
所以选B,使后半句成为分句