() troubles him is () he should ask for help.是二个从句

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What troubles him is who(whom) he should ask for help.
这里有两个从句
What.引导一个主语从句.whom （who) 引导一个表语从句.
让他困惑的是,他该向谁求助.
======以下答案可供参考======
供参考答案1:
What that
就是用一个短语做了主语。
后面又是一个宾语从句。