Present Simple vs Present Continuous
http://www.english-grammar.at/online_exercises/tenses/present_simple_progressive1.htm
http://www.english-grammar.at/online_exercises/tenses/present-simple-progressive6.htm
http://www.english-grammar.at/online_exercises/tenses/present_simple_progressive1.htm
http://www.english-grammar.at/online_exercises/tenses/present-simple-progressive6.htm