What is useful for making several decorative shapes of the same size with acrylic colour?

Correct answer: Guide measurements, equal brush load and equal pressure

The governing concept is controlled repetition. Guide measurements establish the same dimensions, while a similar amount of paint on the brush and steady pressure help each mark have comparable coverage and edges. Thus option C is correct. Using a different brush, drawing without a plan, or changing water quantity introduces variation, so options A, B, and D do not reliably produce equal decorative shapes.