It is helpful to put children in a situation ____they can see themselves differently .

考查什么语法：
这是定语从句,先行词是situation,如果从句中缺少状语,situation后就要用where,这是规定,此处where可译为：在该环境或情况下.
a和c为什么不行：
1.此题中因为括号后的定语从句主谓宾完整,所以就考虑用状语where,答案选B
2.A和C在定语从句中做宾语或主语,也就是关系代词,代替主或宾.而where是关系副词,作状语.而该题定语从句中主谓很完整,因此就选B.
3.when在此不能引导situation.when是：在.时候.where是：在.情况中或形势下.所以以后见到situation,你就要考虑是否用where,但是最近有一种趋势,就是把situation做定语从句的宾语或主语,那样的话就要考虑that和which,例如：
I had to face the situation that they put me in.
这时候用that或which,因为从句中缺少in的宾语,叫做介宾,所以这时候,situation后用that或which都对.
怎么翻译：
该题译为：把孩子们放到这种环境中很有帮助.在该环境中他们能从不同的视角来审视自己.
怎么划分句子成分：
It （形式主语）
is （系动词）
helpful （表语）
to put children in a situation ____they can see themselves differently .（真正主语）
这其实算一个倒装句,to后面的句子才是真正主语,因为主语太长,句子就不平衡,显得头重脚轻,句子还原你看一下：
To put children in a situation where they can see themselves differently is helpful.
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主语 系 表
所以,为了平衡句子,就用了it做形式主语,这样的话,句子就平衡了.
It is helpful to put children in a situation where they can see themselves differently .