How is passive voice in the present continuous tense converted into the past continuous tense?

By changing the main verb

By changing the subject

By changing the tense of the auxiliary verb

None of these

In passive voice, the auxiliary verb "is/are" in the present continuous tense is changed to "was/were" in the past continuous tense.

The main verb remains in the past participle form.

For example:

Active: "The book is being read by the students."

Passive (Past Continuous): "The book was being read by the students."