With sufficient scientific information amanned trip to Mars should be _____

Hard as a teacher may try, he can’t ______to make all his students make a difference in study, letting alone in life.

_______ meet Mr Wang, chairman of the trade union, he waited at the gate of the factory

llution in Beijing is expected to improve, ________ a series of air pollution control measures.

we were listening to the speechattentively, a voice _____ to announce the result of the election.