Which method is more suitable for obtaining an opaque brush stroke?

Correct answer: Use less water and sufficient paint

Opacity means that the paint hides or covers the surface beneath it. Using less water and enough concentrated paint places more pigment in each stroke, so the layer appears solid and opaque; therefore, option C is correct. A large amount of water makes paint transparent, an empty brush leaves little colour, and wet paper usually spreads and weakens the mark rather than making it opaque.