The correct answer as to the structure most responsible for maintaining cell homeostasis would be the plasma membrane. The correct option would, thus, be D.
Homeostasis refers to the maintenance of relatively constant internal processes such as solute concentration, water, etc.
The plasma membrane functions by regulating the movement of substances in and out of the cell.
The normal range of concentration of materials within the cell in which it can function optimally is known as the setpoint.
When the concentration of a particular substance in the cell falls below the setpoint, the plasma membrane would become permeable for the inflow of such substance. Such substance becomes free to move into the cell through diffusion so that the setpoint can be restored.
When the concentration of a particular substance in the cells exceeds the set point, the plasma membrane becomes permeable for the outflow of the substance. The substance, thus, diffuses into the cell until the setpoint is restored.
More on plasma membrane can be found here: brainly.com/question/1578184