Which of the following is the BEST way to maintain the operational environment in a datacenter?

Which of the following is the BEST way to maintain the operational environment in a datacenter?

A.
Seal the room so the outside environment has less impact on the datacenter environment.

B.
Run the systems in “low-power” mode to put less strain on the HVAC unit(s).

C.
Open the doors to the datacenter and run large fans to pull hot air away from the room.

D.
Provide one-for-one backup (n + n) HVAC units so each unit operates more efficiently.