现在进行时怎样变否定

现在进行时的结构是:动词BE(AM/ IS / ARE )+动词ING 形式,所以其的否定形式是直接在BE后加NOT,如:
He is doing his homework -> He isn't doing his homework.

not doing

现在进行时的结构是:动词BE(AM/ IS / ARE )+动词ING 形式,所以其的否定形式是直接在BE后加NOT,如:
I'm playing football. -> I'm not playing football .
He is doing his homework -> He isn't doing his homework.
they're playing football. -> they aren't playing football .