Prepositions of time

https://www.englishclub.com/grammar/prepositions-at-in-on-time.htm

A, AN, THE

http://ingles.about.com/od/gramatica/qt/A-An-The.htm


EXERCISES

http://www.agendaweb.org/grammar/articles-definite-indefinite-exercises.html

Preposition of place

Exercise

http://www.agendaweb.org/grammar/prepositions-exercises.html