count.down
n.（名词）The counting backward aloud from an arbitrary starting number to indicate the time remaining before an event or operation, such as the launching of a missile or space vehicle.倒数报时：从任意的一个数字开始倒着数，以表明距离某件事或操作（例如发射导弹或宇宙飞船）的时间The checks and preparations carried out during this activity.准备过程，准备工作：在倒数报时期间所进行的检查和准备
