Correct option is D
In thermodynamics, a control volume refers to a fixed region in space through which fluid may flow, and it is used for analyzing the behavior of a thermodynamic system. The boundaries of the control volume can be real or imaginary, and within this region, mass and energy can cross the boundary. This concept is fundamental in the study of open systems where the focus is on the flow of fluids and the exchange of energy across the control volume's boundaries, rather than focusing on a specific mass.
