Picture a ferromagnetic block with no field applied, where the tiny magnetic regions called domains point in many different directions, so their fields cancel and the block shows no net magnetism from the outside. As soon as a field is switched on, the domains that already happen to point roughly along the field begin to grow by pushing their boundaries into the neighbouring, unfavourably oriented domains, and the atomic moments inside those domains slowly rotate to line up with the field. As the field strength increases further, this continues until practically the whole sample acts like a single domain pointing along the applied field, which is the saturated state. It is this growing and lining up with the external field, not random pointing or vanishing on cooling, that describes how domains behave. So the correct choice is option (A).