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
网友回答
A. has been launched
(答案→)B. having been launched
C. being launched
D. to be launched
解析：考查独立主格。the most recent spacecraft和launch之间是动宾关系，at the end of last March.表面用完成形式。所以选B。