同学你好，该知识点来自沪江网校《BEC商务英语中、高级连读【6月签约班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学好，
助助总结以下情况，供同学参考哦：
1.当句子主语是被动词“do”作谓语的定语从句修饰的al， all that anything， the only thing(way)，或 thing前面有序数词( first second)或last等修饰，或者是形容词+最高级修饰时，“to”都可以省略。例如

All you have to do is put it in the toaster and wait till it pops up.做的是把面包片往烤炉里一放，便可等它跳起来。
Anything we could do was empty the bottle我们能做的只是把瓶子倒干净。
In the evening the only thing he did was read the newspaper. 晚上他做的唯一的事，是看看报纸。
The only way you can be strong is stand together要强大的唯一办法是闭结起来
All you need to do is press the switch， and the motor starts你要做的只是按下开关，马达就发动

2. 当主语thing被不定时修饰时，to也可以省略，如
The thing for you to do is face the facts.

3. 当主语带do表语省略to的情况：当主语部分有动词do的某种形式时，用作表语的不定式可以省略to。如：
All you need do now is (to) complete the form. 你现在要做的只是把这张表填好。
The only thing to do now is (to) go on. 前进是现在唯一的出路。
What I‘ll do is (to) tell her the truth. 我要做的就是告诉她真相。
What I want to do is take a holiday right away.我想能马上就去度假。

4.当主语“all”被以动词“say”作谓语的定语从句修饰时，其表语的不定式符号“o”也可省略。例如：All they said is hurry up.他们只是说赶快。

祝进步~