题目：
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：
答案：B
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。
