1. I think she is there.
误：I think she isnt there.
正：I dont think she is there.
析：英语中think, believe, expect, suppose等表示信念和揣测的动词，后接that从句时，习惯上将从句中的否定形式转移到主句上，即否定主句谓语，不否定从句谓语。
2. He can sing this song and that one.
误：He cannot sing this song and that one.
正；He cannot sing this song or that one.
析：肯定句中的连词and在否定句中一般要改为or。