Passed is both the past and past participle form of the verb pass. Past is a noun (meaning "a previous time"), an adjective (meaning "ago"), and a preposition (meaning "beyond").
Examples:
The past two weeks have been hard for Sally. She has not passed any of her exams. When she walked past me, I told her to forget the past and look toward the future.
Practice:
(a) We drove _____ the exit five minutes ago.
(b) We _____ the exit five minutes ago.
(c) In the _____, students wore caps and gowns.
(d) In _____ years, students had to do kitchen chores.
