What control is required to make both the vein and broad part of a leaf with one brush?

Correct answer: Change brush angle, pressure and edge use

The governing concept is brush control: the mark changes when the angle, pressure and contacting edge change. Light pressure with a narrow edge can create a thin leaf vein, while greater pressure or a flatter angle uses more bristles to produce the broad blade. Therefore option C is correct. Merely changing colour or washing the brush does not change the mark’s width, and folding the paper is irrelevant.