问题
选择题
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
题目分析：考查独立主格结构：句意：这个国家已经发射了三颗无人飞船，最近的在去年三月份被发射。句中没有连接词，故不能选作谓语动词的A项；由at the end of last March可知应选用表示动作完成the most recent having been launched为独立主格结构，选B项。