Select the option that expresses the given sentence in passive voice.
They are constructing a new building in the city centre.

Correct option is B

The correct passive voice expression is (b) "A new building is being constructed by them in the city centre."
The sentence is in the present continuous tense, and the passive form maintains this tense while shifting the focus from the subject to the action and the object of the action.
Grammatical rule used: In passive constructions, the object of the active verb becomes the subject of the passive verb, and the form of 'be' (is/are) plus the past participle (being constructed) reflects the ongoing action.
Conversion rule:
Present continuous
Subject + is, am, are + verb + ing + object -> <- Object + auxiliary verb (is, am, are) + being + past participle + by + subject.