Forms 6a, 6c. Question words

For practicing:
https://www.englisch-hilfen.de/en/exercises/questions/question_words2.htm;
http://www.english-4u.de/question_words_ex1.htm;
http://www.englishexercises.org/makeagame/viewgame.asp?id=2066;
http://speakspeak.com/english-grammar-exercises/elementary/exercise-interrogative-pronouns.