Third Conditional (3rd grade)

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/3cond.htm 
(to study)

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/3cond1.htm 
(to practice)

http://www.ego4u.com/en/cram-up/grammar/conditional-sentences/type-3/exercises (to practice)