单项选择题What was the aim of the investigation referred to in the passage
单项选择题The most detailed information about the woman robber is her ______.
单项选择题U.S. President urged the U.S. Congress to play a key role in the fight against ______ in Africa.
填空题grammar and vocabulary
单项选择题People did not begin to use unmanned vehicles in undersea exploration until recently because of______.