同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读【特惠班】》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。

同学你好~
occur to sb （观念或想法) 被想到；出现在头脑中
The idea occurred to him in a dream.这个主意是他在梦中想到的。
It didn't occur to him that his wife was having an affair.他没有想到自己的妻子有婚外情。
It didn't occur to her to ask for help. 她没想到请别人帮忙。

这里it是形式主语，to open up the box是不定式短语作主语。
It suddenly occurred to one of the workers to open up the box.  一名工人突然想到打开箱子。

up表示动作的完结，open只是单纯说“开”，而open up强调完全打开了，比如
The doctor opened up his stomach to get at the source of the trouble.
医生给他的胃开了刀，以便找出病根。

其他常用形式主语it的句型有：

(1)It is ＋名词＋从句
It is a fact that … 事实是… It is an honor that …非常荣幸 It is common knowledge that …是常识
It’s a pity that you missed the exciting football match.
多么可惜啊，你错过了一场精彩的足球比赛。

(2)it is ＋形容词＋从句
It is natural that… 很自然… It is strange that… 奇怪的是…
It is uncertain whether he can come to Jenny’s birthday party or not.
他来不来参加简的生日派对，这个不确定。

(3)it is ＋不及物动词＋从句
It seems that… 似乎… It happened that… 碰巧…
It seemed that he didn’t tell the truth.
似乎他没有讲真话。

(4)it ＋过去分词＋从句
It is reported that… 据报道… It has been proved that… 已证实…
It is reported that 16 people were killed in the earthquake.
据报道，在这场地震中，有16人遇难。

此外，it用于表示天气、时间等的句子中作主语的时候，也是形式主语。
It's ten past twelve. 现在十二点十分。

It's our anniversary. 今天是我们的周年纪念日。

祝同学学习进步~