17. If you (wear) ____________ sandals in the mountains, you (slip) ____________ on the rocks.
18. If Rita (forget) _____________ her homework, the teacher (give) _________ her low mark.
19. If they (go) _____________ to the disco, they (listen) ____________ to loud music.
20. If you (wait) ___________ a minute, I (ask) ___________ my parents.