单项选择题
How long does it take the spacecraft to go round the Earth（）
A．Forty minutes. B．Fifty minutes. C．Ninety minutes. D．Twenty-four hours.
单项选择题 To relax himself before sleep, the writer often（）
单项选择题 Why can all the astronauts sleep at the same time（）
单项选择题 When the astronauts are working, sleeping bags are fastened（）
