但就在不到一年前，罗伊的父亲被汽车撞伤了。

　　knock at/on the door 敲门

　　knock down 撞倒；拆除

　　knock...into... 把......插进，把......敲入

　　knock into/against 撞上

　　①Knock down the machine before shipping.

　　在装运前把机器拆卸开来。

　　②Listen！Someone is knocking at/on the door.

　　听！有人在敲门。

　　③Be careful！Don't knock against/into the wall.

　　当心！不要撞到墙上。

from time to time偶尔，有时

　　(教材P30)These days，Roy and I see each other from time to time，but we're no longer close.

　　最近，我和罗伊还时而见面，但已经不再那么亲密了。

,

　　①He called at our home at times.

　　他有时到我们家玩。

　　②She was a nurse at one time.

　　她曾经是个护士。

　　③If you don't work hard，you'll regret it in time.

如果你不努力学习，你迟早会后悔的。