the negative forms of "to be"

http://www.eclecticenglish.com/grammar/PresentSimpleToBe1B.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=8213
http://www.englishexercises.org/makeagame/viewgame.asp?id=8301
http://www.englishbee.net/lessons/basic_exer/tobe/to_be_negative/verb_to_be_negative.htm
https://www.montsemorales.com/gramatica/Benegative.htm
http://www.perfect-english-grammar.com/present-simple-exercise-10.html

Use the positive or negative forms of "to be"
http://www.englishmaven.org/HP6/To_Be_Exercise4.htm
http://www.englishmaven.org/HP6/To_Be_Exercise3.htm