把定语从句连同引导词一起拿出来,把引导词去掉,看这个句子是不是缺少主语 宾语 表语 ,如果不缺少,就是完整了.

如：

This is the book that I bought yesterday.

that I bought yesterday

去掉that:I bought yesterday（少了宾语）

The house is where I used to live.

where I used to live

去掉where:I used to live句子完整.

不管是什么从句,它必须有被修饰的主体,从句本身是主谓宾存在的!而且主句和从句的时态须一致.