If I ____________ (study) harder in school, I _____________ (graduate) university.
If I had studied harder in school, I would have graduated university.
If the police _________ (catch) him, he __________ (go) to jail.
If the police had caught him, he would have gone to jail.
If I __________ (remember) your birthday, I _________ (buy) a present.
If I had remembered your birthday, I would have bought a present.