if后面加do还是doing

if后面加do还是doing，都是可以的。在含有条件状语从句的复合句中，表示将来时态，主句是一般将来时态，祈使句或情态动词，if后的从句要用现在时态，与现在事实相反if从句谓语用过去式或者were，与过去事情相反if从句谓语用过去完成时为had+过去分词，与将来事实相反if从句谓语用动词过去式为should+动词原形，或wereto+动词原形。

I can give you a round neckline if you prefer.

如果您喜欢我可以给您开个圆领口。

If these terms are not acceptable to you,we may suggest others.

如果你对这些条件不合意，我们可提出别的条件。

If she needs salvation,she will posit a savior.

如果她需要救助，她就会设想一个救助者。

If you were a bird,you could fly.

如果你是鸟，你就能飞行了。

I should have talked to mother if I had thought of it.

如果当初我想到了，我就和妈妈说了。

if only.要是……多好……if not不然的话

as if.犹如，好像……if any若有的话

only if.只有当if and when如果

if possible.如有可能if necessary必要时

what if.如果……将会怎……if you like如果你愿意

1、I could do it now,if you like.

如果你愿意的话，我现在就可以做这事。

2、You can come with us if you want to.

如果你愿意可以跟我们一起来。

3、Put your hand up if you need more paper.

若有人还要纸，请举手。

4、If that is the case,we need more staff.

如果真是那样，那我们就需要更多的员工了。

5、If that is the case,we need more staff.

如果真是那样，我们就需要更多的员工了。

6、Let me know if you have any problems.

你若有困难就告诉我。

7、I went to see if my old school was still there.

我去看过母校是否依然存在。

8、Call me if you have any problems regarding your work.

你如果还有什么工作方面的问题就给我打电话。

9、If you should change your mind,do let me know.

假如你改变主意的话，一定要告诉我。

10、What difference will it make if he knows or not?

他知不知道有什么关系吗？

11、I can't work if I'm cold.

我要是觉得冷就干不了活。

12、If you have any issues,please call this number.

如有问题，请拨打这个电话号码。

13、She asked me if I would give her English lessons.

她问我愿不愿意给她上英语课。

14、Perhaps it would be better if you came back tomorrow.

如果你明天回来，也许更好。

15、That was a disaster if ever there was one!

那确实是场灾难！

16、I'll get there,even if I have to walk.

我就是走也要走到那儿去。

17、If we take the lead in this,others may follow.

如果我们在这方面带头行动，其余的人就会跟着来。

18、Put your hand up if you know the answer.

知道答案就举手。

19、If he can't help,there's always John.

如果他帮不上忙，总还有约翰呢。

20、If you love each other,why not get married?

要是你们彼此相爱，干吗不结婚呢？