What action is required to make a broad stroke with a round brush instead of using only the tip?

Correct answer: Spread more of the bristles on the surface with pressure

The governing concept is control of brush contact. A round brush makes a fine mark when only its pointed tip touches the surface, but applying suitable pressure bends and spreads more of the bristles, increasing the contact area and producing a broader stroke. Therefore option D is correct. The handle, an unloaded brush, or movement in the air cannot create a painted broad mark.