What may cause visible brush streaks in a colour layer?

Correct answer: Uneven paint consistency or heavy pressure

The governing concept is achieving an even paint layer through consistent mixture and pressure. If the paint is too thick in some places, too thin in others, or the brush is pressed heavily, the bristles leave tracks that remain visible as streaks. Thus, option C is correct. Light paper, a large picture, or a round palette does not directly create brush marks. Mixing the paint evenly and using moderate, consistent pressure helps produce a smoother surface.