The correct answer is D. Possesses internal stresses.
A pre-stressed concrete member is a concrete member that has been subjected to internal stresses before it is subjected to external loads. This is done by applying tensile forces to the concrete before it is cast, which causes the concrete to develop compressive stresses. These compressive stresses help to counteract the tensile stresses that are caused by the external loads, which makes the member stronger and more resistant to failure.
Option A is incorrect because not all pre-stressed concrete members are made of concrete. Some pre-stressed concrete members are made of reinforced concrete, which is a composite material that consists of concrete and steel reinforcement.
Option B is incorrect because not all pre-stressed concrete members are made of reinforced concrete. Some pre-stressed concrete members are made of plain concrete, which is concrete that does not contain any steel reinforcement.
Option C is incorrect because not all pre-stressed concrete members are stressed after casting. Some pre-stressed concrete members are stressed before casting, and some are stressed after casting.