你的理解没问题,但是,你记错了。当主句的主语是第一人称时,且谓语动词是think/ guess/ suppose/ imagine的否定形式的时候,反意疑问句跟宾语从句的谓语相一致。其他人称照旧。
如: i don't think he will come ,will he?
she doesn't think you will help her, does she?
Believe是相信的意思,doesn't believe不相信,是否定。前肯定,后否定,选b
这个应该是约定成俗的啊