Present Forms

Present forms:

http://www.better-english.com/grammar/presforms.htm

Present Perfect vs Simple Past:

http://www.english-grammar-lessons.com/presentperfectorpastsimple/exercise2.html

http://www.english-grammar-lessons.com/presentperfectorpastsimple/exercise4.html

http://www.english-grammar-lessons.com/presentperfectorpastsimple/exercise5.swf