The answer is B, the diaphragm and the rib cage return to their normal position.
When you breathe in, which is inhalation, the diaphragm will move downwards, and get flattened. The rib cage will move upwards and outwards. The whole purpose of this is to increase the lung volume, so that more air could rush in.
But during exhalation, air should be forced out of the lungs, so, the diaphragm returns to its dome shape, which it moves upwards, and the rib cage moves downwards and inwards.
Therefore, the answer to this is B.
