Passive Voice

The rule is be + past participle.

You have to pay attention to the verb tense used in the active sentence, because the verb "to be" will be always in that tense.

Present Simple

Active: He repairs the car.

Passive: The car is repaired.

Past Simple

A: He repaired the car.

P: The car was repaired.

Present Continuous

A: He is repairing the cars.

P: The cars are being repaired.

Past Continuous

A: John and Fred were repairing the cars.

P: The cars were being repaired by John and Fred.

Future Simple

A: Jess will repair the car.

P: The car will be repaired by Jess.

Future "Be going to"

A: They are going to repair the car.

P: The car is going to be repaired.

Present Perfect

A:He has repaired the car.

P: The car has been repaired.


Past Perfect


A: She had repaired the car.

P: The car had been repaired.

Modal

A: They should repair the car.

P: The car should be repaired.

Try this:
http://web2.uvcs.uvic.ca/elc/studyzone/410/reading/exercises/dogqz.htm