"What"在句子中通常用作引导一个疑问句或从句，用来询问或指代某个事物、抽象概念或事件。
1、What+主语+及物动词：
例句1：What he says is reasonable.
他说的很有道理。
解析：What he says是主语从句，what 在主语从句中作宾语。
例句2：It is none of your business what other people think about you. Believe yourself.
解析：本句意为“别人怎么看你，与你无关，相信你自己。”其中It是形式主语，真正的主语是what other people think about you.
2、what +主语+不及物动词/系动词+介词：
例句：The judge does not consider what each eyewitness looks like.
法官没有考虑每个目击者的长相。
解析：what each eyewitness looks like是宾语从句，what在从句中作介词like的宾语。
3、What + 主语+系动词：
例句1：He is not what he was ten years ago.
解析：本句意为“他不再是十年前的他了。”其中what he was是表语从句，what 在从句中作表语。
例句2：I’m not to blame, Mum. I am what you have made me.
不怪我，妈妈。是你造就的我。
解析：what you have made me.是表语从句，what 在从句中作补语。
例句3： The seaside here draws a lot of tourists every summer. Warm sunshine and soft sands make what it is.
这里的海滨每年夏天都吸引很多游客。温暖的阳光和柔软的沙子造就了它。
解析：what it is是宾语从句，what 在从句中作表语。