Was and Were

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

Was or Were

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

Don't, doesn't, didn't

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

Verb be

http://a4esl.org/q/j/jb/mc-be.html

Do, Does, Did

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