I don't think Jim ____(look)like his mother.为什么是“looks"?不是否定句吗?

I don't think Jim ____(look)like his mother.为什么是“looks"?不是否定句吗?
I don't think Jim ____(look)like his mother.为什么是“looks"?
不是否定句吗?

I don't think Jim ____(look)like his mother.为什么是“looks"?不是否定句吗?
否定已前移,从句的主语是第三人称单数,故要用looks