In order to convert the given question into passive voice, let's understand the difference between active and passive voice.

Active voice emphasises on the person who does the action, whereas passive voice emphasises on the action itself. For example:

Active: The thief stole my car.

Passive: My car was stolen by the thief.

The object 'My car' comes first and the subject 'the thief' is put after the verb in the passive voice.

The receiver of the action in the given sentence is: 'the luggage'

In the passive voice, the receiver becomes the subject. Right after the subject, we place a verb and then the receiver of the action (object) and the remaining clause, if any. We also use 'by' before the object to show that the action was performed by the object.

As the given sentence in the active voice is in the past continuous tense, we will use 'was/were' and 'being' with the verb in the past participle form to form the sentence in the past continuous tense in the passive voice.

Hence, 'The luggage was being carried by the porter.'

Thus option A, B and C are incorrect.

CORRECT ANSWER - D - 'The luggage was being carried by the porter.'