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：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。