Present vs. Present Continuous

sxs--I smile when I'm happy
SxS Video--Why are you washing dishes in the bathtub?

English Language Centre's explanation and quiz

University of Victoria Written Explanation

Using English Practice ID and use of simple present vs. present progressive

Quiz-style exercise from Learn English Feel Good

University of Victoria Quiz-style exercises

English Hilfen de Quiz

Learn English Feel Good Quiz

English 4U Quiz

http://www.learnenglishfeelgood.com/simple-present-present-continuous3.html

Using English Quiz

Actually, when you smile is better grammar than when you're smiling.