Grammar

Prepositions

https://owl.english.purdue.edu/exercises/2/14

Tense

https://owl.english.purdue.edu/exercises/2/22/49/

Consistency of tenses quiz

http://www.bristol.ac.uk/arts/exercises/grammar/grammar_tutorial/page_75.htm

Prepositions:

http://www.perfect-english-grammar.com/prepositions.html

Quiz

http://www.rong-chang.com/ex/preposition01.htm

Quiz:

http://a4esl.org/q/h/mc006-ck.html