Van gogh builds up his lines in thick, bold strokes that possess an almost structural quality known as

The answer to this quesiton is impasto
impasto is a form of painting technique that laid the paints on a surface area with very thick layers. The main purpose of this technique is to make sure that the brush or painting-kinfe strokes are visible and paint could mixed easily onto the canvas

Ibelieve that the answer is (a).

Absolute