The country has already sent up three unmanned spacecraft the most recent at the end of

问题补充：

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：

A. has been launched

(答案→)B. having been launched

C. being launched

D. to be launched

解析：

这题考查独立主格结构，结构是：名词+非谓语，此句前后句没连词，只有逗号是不能连接两个句子的,所以后边the most recent at the end of last March就是独立主格的形式了，在句中做伴随状语，又因为事情发生在过去，所以用现在分词完成时。选B。