http://study.com/academy/lesson/using-the-imperfect-subjunctive-with-the-conditional-in-spanish.html
impt subj: http://www.spanishdict.com/topics/practice/98
http://www.indiana.edu/~call/ejercicios/imp_imp_subjuntivo01.html
http://www.indiana.edu/~call/ejercicios/prac_sub_imp02.htm
http://web.abo.fi/csk/proj/vkk/caminando/5/recordando/subj_imperfectocondicional_simple.htm
http://www.aprenderespanol.org/verbos/subjuntivo-imperfecto.html
https://espanol.lingolia.com/en/grammar/subjuntivo/preterito-imperfecto/exercises
http://www.ver-taal.com/ej_subjuntivoimperfecto_uso1.htm
http://www.mhhe.com/socscience/spanish/puntos/graphics/puntos_6e/ch18/others/gram18_2.htm
http://www.todo-claro.com/castellano/avanzados/gramatica/El_subjuntivo_imperfecto/Seite_3.php
http://www.indiana.edu/~call/ejercicios/imp_imp_subjuntivo01.html
https://www.spanishdict.com/quizzes/98/spanish-imperfect-subjunctive
https://www.quia.com/quiz/363744.html?AP_rand=1185555255
https://www.learnspanishfeelgood.com/spanish-if-clauses-conditional3.html
https://www.lawlessspanish.com/tests/siclauses-test.html
https://www.123teachme.com/spanish_sentence_quiz/category/If_clauses