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
独立主格结构作状语，排除谓语动词形式，即A项。“the most recent”与“launch”为逻辑上的被动关系，且“launch”在谓语动词之前发生。