Choose the most appropriate option to change the voice (active / passive) form of the given sentence.
Popular monuments will be kept open till 9 p.m.

A

They had kept popular monuments open till 9 p.m.

B

They are keeping popular monuments open till 9 p.m.

C

They will keep popular monuments open till 9 p.m.

D

They will be keeping popular monuments open till 9 p.m.