Control volumes refer to: A a fixed region in space B a specified mass C an isolated system D a closed system

http://en.wikipedia.org/wiki/Control_volume

In fluid mechanics and thermodynamics, a control volume is a mathematical ... In an inertial frame of reference, it is a volume fixed in space or moving with ...

Therefore my answer is A

A , and that is mor or less D also?

Agree with Mr. Tartir

A a fixed region in space  

Control volumes refer to a fixed region in space. So choice A is the correct answer.

Option A