Grammar 1

Do-Does-Did

http://a4esl.org/q/h/lb/dodoesdid.html

Am-Are-Is

http://a4esl.org/q/f/x/xz85mbs.htm

Don't-Doesn't-Didn't

http://a4esl.org/q/h/lb/dontdoesnt.html

Have-Has

http://a4esl.org/q/h/lb/have.html