pay的用法pay back，pay off，pay 有什么本质区别

1. pay
   1）vt.支付,付；偿还,补偿
   I must pay her.我应该付她钱.
   If you do not pay the
   rent,the landlord will kick you out.
   如果你不付房租,房东就会把你撵出去.
   The sale of the
   house should fetch in enough to pay our
   debts.
   出售这栋房子足以付清欠我们的债.
   2）vi.付款；偿还
   I'll settle with you,you have to pay
   for your insulting.
   我早晚要找你算这笔账的,你得为你的侮辱行为付出代价.
   3）n.工资,薪水；付款
   Part of
   their pay is taken out in houses.他们的部分工资是以住房偿付的.
   2.pay off,付清,还清(债务)
   Pay
   off your credit cards.还清你的信用卡欠款.
   Though it still takes time to pay off your
   debts,you begin to see results almost
   immediately.
   虽然这依旧要花很多时间去偿还你的债务,但你很快就会看到结果.
   3.pay back偿还,报复
   Some day
   I'll pay you back for this!
   总有一天我会为此报复你的!

   
   

pay的基本用法是： 

(1) pay (sb.) money for sth. 付钱（给某人）买……。例：I have to pay them 20
pounds for this room each month. 我每个月要付20英磅的房租。

 (2)pay for sth. 付……的钱。例：I have
to pay for the book lost. 我不得不赔丢失的书款。 

(3)pay for sb. 替某人付钱。例：Don?蒺t
worry!I'll pay for you. 别担心， 我会给你付钱的。 

(4)pay sb. 付钱给某人。 例: They pay us
every month.他们每月给我们报酬。

（5）pay money back 还钱。例：May I borrow 12 yuan from you?
I'll pay it back next week. 你能借给我12块钱吗？下周还你。

（ 6）pay off one's
money还清钱

cost 和pay的区别

spend，cost，take和pay都可以表示“花费”，但用法却不尽相同。

spend的主语必须是人， 常用于以下结构：(1) spend
time ／money on sth. 在……上花费时间（金钱）。例：I spent two hours on this maths problem.
这道数学题花了我两个小时。(2) spend time ／ money (in) doing sth. 花费时间（金钱）做某事。例：They spent two
years (in) building this bridge. 造这座桥花了他们两年时间。(3)spend money for sth.
花钱买……。例：His money was spent for books. 他的钱用来买书了。

cost的主语是物或某种活动，
还可以表示“值”， 常见用法如下：(1)sth. costs (sb.) ＋金钱,某物花了（某人）多少钱。例：A new computer costs a
lot of money. 买一台新电脑要花一大笔钱。(2) (doing) sth. costs (sb.)
＋时间,某物（做某事）花了（某人）多少时间。例：Remembering these new words cost him a lot of time.
他花了大量时间才记住了这些单词。

注意：cost的过去式及过去分词都是cost,并且不能用于被动句。

take后面常跟双宾语，
常见用法有以下几种：

(1) It takes sb. ＋时间＋to do sth. 做某事花了某人多少时间。例：It took them three years
to build this road. 他们用了三年时间修完了这条路。

(2)doing sth. takes sb.
＋时间,做某事花了某人多少时间。例：Repairing this car took him the whole afternoon. 他花了一下午修车。  

pay 支付，付款，缴纳
Please pay your bill. 请付账。/请买单。

pay off 付清，还清
He paid off the debt of his friend. 他还清了他朋友欠下的债。

pay back 偿还，回报，报答
I'll pay her back for her hospitality by inviting me to dinner.我要请她吃饭以回报她的殷勤款待。

1.pay
1）vt.支付,付；偿还,补偿
I must pay her.我应该付她钱.
If you do not pay the rent,the landlord will kick you out.
如果你不付房租,房东就会把你撵出去.
The sale of the house should fetch in enough to pay our debts.
出售这栋房子足以付清欠我们的债.
2.pay off,付清,还清(债务)

Pay off your credit cards.还清你的信用卡欠款.
Though it still takes time to pay off your debts,you begin to see results almost immediately.
虽然这依旧要花很多时间去偿还你的债务,但你很快就会看到结果.
3.pay back偿还,报复
Some day I'll pay you back for this!
总有一天我会为此报复你的!

前者是偿还，后者是还清