What may be the main cause of paint bleeding under a stencil in acrylic painting?

Correct answer: Paint that is too thin or an overloaded brush

Stencil edges work best when paint is applied in a controlled, fairly small amount. The governing technique is preventing capillary seepage and excess paint from travelling beneath the edge. Thin paint or an overloaded brush supplies too much mobile liquid, so option A is correct. A firmly held stencil and light dabbing with a small amount reduce bleeding; a dry surface with little paint is not the main cause.