当暖而轻的空气上升时,周围冷而重的空气便下降来补充,这种升降运动称为()。
参考答案:对流
He didn't want to see anybody, so he spent six hours ________ in the small room.
A.locked
B.to lock
C.locking
D.being locked
____ 时期,古典小说的创作进入成熟阶段。