In August 1977, a satellite _______ to gather data about the 10

In August 1977, a satellite _______ to gather data about the 10 million black holes which are thought to be in the Milky Way.
A、launched
B、was launched
C、has been launched
D、is launched
【正确答案】：B
【题目解析】：句意：1977年8月，一颗卫星被发射升空，以收集有关银河系中1000万个黑洞的数据。