句子中am是谓语动词,on the sofa是状语,sit也是动词,一个句子中不能有两个谓语动词,如果非要加进去的话可改为I am whathing TV,siting on the sofa,“siting on the sofa”作状语,不过这样改很没必要啦,原句就好,主谓宾状齐全了~