单选题 The children went there to watch the iron tower ______.

单选题 The atmosphere of the earth is ______ the moon.

单选题 Bats begin their flight as soon as the sun begins to sink ______ the horizon.

单选题 Peter was ______ diligent than Jack because both of them failed the final examination.

单选题 "Hurry up, or the tickets ______ out by the time we get there."

单选题 Human beings are superior to animals ______ they can use language to communicate.

单选题 ______ on a clear day, far from the city crowds, the mountain gives him a sense of peace.

单选题 Only when you have obtained sufficient data ______ come to a sound conclusion.