Which brush is more useful for covering a large area with acrylic colour?

Correct answer: Wide flat brush

The governing brush-selection concept is that brush size and shape should match the area and finish required. A wide flat brush carries enough acrylic paint to cover a broad surface in fewer, more even strokes, so option C is correct. A liner brush is designed for fine lines, a dry broken brush gives a rough texture, and a pointed pen is not a suitable acrylic painting brush.