he should cut his hair.(改为被动语态）

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He should have his hair cut.因为他自己不能剪自己的头发,其中有个第三者,用have sth done用法.“ 主语+have+宾语+过去分词”
在“have sth done”结构中,have 有“请,让,使”的意思,由过去分词充当宾语补足语.
类似用法,如：
I want to have my bike repaired.
我想把我的自行车拿去修理.
======以下答案可供参考======
供参考答案1:
His hair should be cut by him
情态动词的被动语态，在情态动词后+be+动词的过去分词
供参考答案2:
His hair should be cut.
主动句这样讲更好：He should have his hair cut.
供参考答案3:
His hair should be cut by him
供参考答案4:
His hair should be cut by him