She fell while toddling around.她边蹒跚学步边摔倒了。
You can go swimming while I'm having lunch.我可以去游泳,而你则可以吃午饭。
David rang up while you were out.你不在家的时候,大卫打电话来了。
wait for a while 等一会儿
after a while 隔了一会儿