keep

keep somebody back（宾语在back前面）阻挡，拦阻，制止其前进：

Frequent illnesses kept him back.

经常生病使他进展迟缓。

keep down（tr）压抑，控制：

What is the best way to keep down rats？（keep them down）

控制鼠患的最佳方法是什么？

Try to remember to turn off the light when you leave the room.I am trying to keep down expenses.（keep expenses down）

你离开时，要记得熄灯。我在努力控制支出。

keep off（tr/intr）避免在……上践踏，避免来到近旁：

‘Keep off the grass.'

“禁止践踏草地！”（公园里的布告）

keep on 继续，不停歇：

I wanted to explain but he kept on talking and didn't give me a chance to say anything.

我本想解释一下，可是他不住嘴地说，不给我说话的机会。

keep out（tr）阻止进入，挡住：

My shoes are very old and don't keep out the water.（keep the water out/ keep it out）

我的鞋很旧，漏水进去了。

keep out（intr）不许进来，留在外面：

‘Private.Keep out.'

“私人产业。不许进入。”（门上的告白）

keep up（tr）继续保持（努力）：

He began walking at four miles an hour but he couldn't keep up that speed and soon began to walk more slowly.（couldn't keep it up）

他开始以每小时四英里的速度走路，但是无法维持那个速度，不久之后就放慢了脚步。

It is difficult to keep up a conversation with someone who only says‘Yes'and‘No'.

与光说“对”和“不对”的人很难把谈话继续下去。

keep up（intr），keep up with（tr）与某人齐头并进，和某人同速前进：

A runner can't keep up with a cyclist.

跑步的跟不上骑车的。

The work that the class is doing is too difficult for me.I won't be able to keep up（with them）.

班上学的东西对我讲是太难了。我跟不上（他们）。

It is impossible to keep up with the news unless you read the newspapers.

你要是不读报，就跟不上时事。

knock

knock off（tr/intr）（一天的活干完之后）歇了，收工，下班（俗语）：

English workmen usually knock off at 5.30 or 6.00 p.m.

英国工人一般在下午5点半或6点下班。

We knock off work in time for tea.

我们收工后，正好能赶上喝下午茶。

knock out（tr）重击使之晕倒在地：

In the finals of the boxing championship he knocked out his opponent，who was carried out of the ring.（knocked his opponent out/knocked himout）

在拳击锦标赛决赛中，他把对手击昏在地，后者被人抬出了拳击台。