单项选择题
A．there is no life there now
B．there is a large amount of water at the poles
C．the Mars may be able to support life in the future
D．conditions may have been similar to those on the Earth
单项选择题 I am very grateful to you for what you"ve given me and ______ you have done for me.
单项选择题 Jean did not have time to go to the concert last night because she was busy ______ for her examination.
单项选择题 The concert usually takes place at the People"s Square, with the audience ______ on the ground.