Form 8c. Past Perfect. Past Simple

Exercises for practicing:
https://www.ego4u.com/en/cram-up/grammar/past-perfect-simple/exercises;
http://www.perfect-english-grammar.com/past-perfect-exercise-1.htm;
http://www.englisch-hilfen.de/en/exercises/tenses/past_perfect_simple_past.htm;
https://www.ego4u.com/en/cram-up/grammar/simpas-pasper;
http://www.englishpage.com/verbpage/verbs13.htm;
https://www.ego4u.com/en/cram-up/grammar/simpas-pasper.