The correct answer is D. All of the above.
According to the steel beam theory of doubly reinforced beams, tension is resisted by tension steel, compression is resisted by compression steel, and the stress in tension steel equals the stress in compression steel.
Tension steel is the steel reinforcement that is placed in the tension zone of a beam. The tension zone is the area of the beam that is in tension, or being pulled apart. The tension steel resists the tensile forces in the beam.
Compression steel is the steel reinforcement that is placed in the compression zone of a beam. The compression zone is the area of the beam that is in compression, or being pushed together. The compression steel resists the compressive forces in the beam.
The stress in tension steel equals the stress in compression steel. This is because the tension and compression forces in a beam are equal and opposite. The tension steel and compression steel must be able to withstand these forces in order to prevent the beam from failing.
Here is a diagram of a doubly reinforced beam:
[Diagram of a doubly reinforced beam]
The tension steel is shown in red and the compression steel is shown in blue. The arrows show the direction of the forces in the beam.
I hope this helps!