knock down 撞倒击倒 knock out 击倒 knock into sb撞在某人身上 knock off敲掉

he didn't obey the traffic rules,so he was knocked down by a truck

knock over
碰翻; 打倒
Coming too fast down the road,I knocked over a child on a bicycle.
由于车开得太快,我把一个骑自行车的小孩撞倒了.
使吃惊
The unexpected news fairly knocked me over.
那意外的消息着实使我吃了一惊.
轻易击败
We should be able to knock the other team over without any trouble.
我们应该能够毫不费力地击败对手.
偷窃; 抢劫
“Where did you get all these watches?Did you knock them over?”“Yes,we knocked over a jeweler's shop last night.”
“你从哪儿弄来这些手表?是不是抢的?”“是的,昨晚我们抢劫了一家珠宝行.”
快速完成
Mike can knock over three or four of those simple drawings in a day.
迈克一天可完成三四张那样简单的图画.
knock down
〈非正〉击倒,撞倒
He knocked his opponent down with one blow in the competition.
比赛中他一拳就打倒了他的对手.
拆卸
The portable device easily knocks down.
这种轻便装置容易拆卸.
〈非正〉降价; 减少
The man was asking ￡5 for the dress,but I knocked it down to ￡4.50.
那件衣服卖主索价5英镑,但我砍价后以4.5英镑买下了.
卖时以击锤表示卖出
The auctioneer knocked the bureau down to a furniture dealer from York.
拍卖者将写字台卖给从约克来的家具商.
〈俚〉挣得,获得过
A clever lawyer can knock down 40,000 dollars in a good year.
如果碰上好运气,一个精明的律师一年就能赚四万美元.
〈俚〉偷; 抢
He wanted to knock down a bank.
他想抢劫银行.
使降低; 使丢脸
She does not want to knock down his self-esteem.
她不想挫他的自尊.
拒绝
They knocked down the suggestion.
他们把这条建议否决了.
挥霍
She knocked down forty dollars at a restaurant.
她在一家饭馆花掉40美元.
在燃烧区域边缘控制〔减弱〕火焰〔高温〕
There was a low protecting wall to knock down the heat blasting from the pit of the furnace.
有一堵低矮的护壁挡住从炉膛里喷出的火焰.

其实这个词语是knock down,后面的doors是根据要表达的意思加上的.
knock down本身是打到,击败的意思.
这句话是：我们只有走出去,打破藩篱（也就是原来的各种束缚）,才能创造新的机会.
或者这句话的本身意思就是：我们只有想办法出去,把门打开才能创造机会
造句比如：
We are going to knock down those old buildings．我们不久就要拆除那些旧建筑物.

及物动词（vt）是指能够直接加宾语的动词
不及物动词（vi）是指如果要在后面加宾语,则需要在动词和宾语之间加介词
所以这里knock是及物动词
可以改的

knock off 是敲落,knock down是击倒、撞倒的意思,其实基本都一样,但是knock off还有中止的意思,而knock down还可以指投篮命中

1 in existence
2 was knocked down
3 move out of her way
4 is worthy
5 in reply
6 in good condition
7 dates back to

1.break into 意思是“强行闯入”.
A thief broke into my house yesterday evening.昨天晚上有一个小偷闯入我家.
2.break out 意思是“爆发、突然发生”.
A fire broke out after we had gone home．在我们离开家后突然发生大火.
3.break away 意思是“突然离开、戒除”.
You must break away from bad habits．你必须戒除坏习惯.
4.break down 意思是“发生故障”.
My car suddenly broke down when I drove to America.当我开车去广州的时候,车突然抛锚了.
5.knock down 意思为“撞到”.
He ran so fast that he knocked an old man down.他跑太快了以至于撞到了一个老人.

knock down 主要是指物理上的伤害
tear down 主要是指精神上的伤害