宾语从句改变形式时该改主句还是从句?变为否定句要看情况,变为一般疑问句时改主句.
I know that Tom comes from America.
----I don't know that Tom comes from America.我不知道汤姆来自美国.
----I know that Tom doesn't come from America.我知道汤姆不是来自美国.
----Do you know that Tom comes from America?你知道汤姆是来自美国的吗?