I think (that) it will clear up this afternoon and that they will come to say goodbye to us.

我认为今天下午天会放晴，他们会来向我们告别的。

三、其他的省略情况

(一)动词不定式的省略

1．当不定式在形容词afraid，anxious，eager，glad，happy，ready，willing等后作状语时，to后的内容常省略。

You can't force him to answer the question if he's not ready to (answer the question)．

如果他不愿意回答这个问题，你不能强迫他。

2．某些使役动词，如：make，let，have等和感官动词，如：see，watch，notice，observe，hear等后面作宾补的不定式须省略to，但若这些动词用于被动语态，则to不能省略。

We often hear her sing an English song in the classroom./She is often heard to sing an English song in the classroom.(被动语态)

我们经常听见她在教室唱英文歌。

3．多个不定式并列时，从第二个不定式开始，可以省略不定式符号to。但若两个不定式之间表示对比关系时，则不能省略to。

I told him to sit down and (to) wait for a moment.

我告诉他坐下等一会儿。

To go home or to stay at school during the weekend has not been decided.

周末回家还是待在学校还没有决定。

4．当不定式在某些动词后作宾语时，to后的内容常可省略。常见的动词有agree，afford，expect，forget，hope，know，manage，pretend，remember，refuse，want，wish等。

I would do it for you，but I don't know how to (do it for you)．

我愿意为你做这件事，但是我不知道怎么去做。

5．介词but，except (除了) 前有实义动词do的某种形式时，后面的不定式省略to。

All he could do was nothing but wait and see.

他所能做的只有等着瞧。

6．当不定式在be going to，be able to，have to，ought to，used to后作复合谓语时，不定式可省略，但要保留不定式符号to。

They didn't visit their parents as much as they ought to (visit their parents)．

他们应该多看望父母，但他们没有。

[名师点津]　①省略的不定式内容若含有作助动词用的have或be的任何形式时，to后要保留原形的have或be。

②类似这样用法的还有动词短语ought to，be going to，be about to，be supposed to，have to