1. 首先down有降低的意思比如：knock down: 降价、下跌：

　　例子：

　　The market might abandon the stock, and knock down the price.

　　市场可能会抛售股票，从而令其股价下跌。

　　2. knock down还有倒下的意思：

　　He was knocked down by a car.

　　他被车撞到了。

　　The suspect was gunned down by the police.

　　嫌疑人被警察击倒了。

　　3. down在动词词组里面还有阻止、抑制的意思。

　　比如turn down:

　　I turned down the job offer.

　　我拒绝了这个工作机会。

　　4. down在动词词组里面还有不工作的意思。比如：

　　The computer breaks down occasionally. We need to buy new ones.

　　电脑经常坏，我们需要买新的。

　　I need to shut down the computer and take a nap.

　　我要关电脑休息会儿。

　　5. down： 心情压抑

　　The weather is getting me down.

　　这个天气让我很不开心。

　　6. 侮辱、低看一眼

　　He looks down on her and doesn't show any respect to her.

　　他看不起她而且很不尊敬她。

　　I cannot believe that she puts him down like that.

　　我不敢相信她如此的揶揄他。