Question

A house is being constructed by them. Change into passive voice

Answer 1

The question is already in Passive Voice.

Active Voice : $<b>They are constructing a house.</b>$

Answer 2

The answer is “A house construction is being done by them.

Here the meaning of the changed sentence has been kept the same whereas the mode of the sentence has been maintained into passive voice.  

The tense is kept as same.

If the sentence has to be changed into an active voice, the answer would have been “they are constructing a house”.