正襟危坐zhèng jīn wēi zuò
参考答案：
襟：衣襟；危坐：端正地坐着。整一整衣服，端正地坐着。形容严肃或拘谨的样子.
社会文教费
Where have men traveled in a spaceship
A. To other planets. B. To the moon. C. Only on the earth.
