Sentences in the past continuous tense can be written in the passive voice.

The Past Continuous Tense

was/were …ing
They were eating the birthday cake

The Passive Voice

The passive voice is made by:
be (in correct tense) + p.p.

So for the past continuous it is:
was/were being …ing

– example

The birthday cake was being eaten

Sentences in the past continuous tense and passive voice

(active) He was cleaning her bike when I visited
(passive) Her bike was being cleaned by him when I visited

(active) a tiger was eating his dog when he came home
(passive) his dog was being eaten by a tiger when he came home

Exercises

1. Change these sentences into the passive voice:
(i) She was washing the dog when it ran away.
(ii) The typhoon was blowing the furniture down the street when they came home.
(iii) The teacher was teaching the class when the fire alarm rang.

2. Change these sentences out of the passive voice:
(i) Four lions were being chased by 100 wildebeest.
(ii) The house was terrible: rain water was being collected by a bucket in the middle of the room.
(iii) The suspected thieves were being watched by the detectives as they walked towards the bank.