Change of Voice - Verbal and Reasoning

Directions to SolveIn the questions below the sentences have been given in Active/Passive voice. From the given alternatives, choose the one which best expresses the given sentence in Passive/Active voice.
Q1:

They have built a perfect dam across the river.

A Across the river a perfect dam was built.

B A perfect dam has been built by them across the river.

C A perfect dam should have been built by them.

D Across the river was a perfect dam.

ANS:B - A perfect dam has been built by them across the river.

No answer description is available.