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
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B解析the most recent having been launched构成独立主格结构。the most recent指最近发射的载人飞船,与launch是被动关系所以要用动词+ing形式的完成式的被动式。