A spreader-sticker added to a spray solution causes the chemical to:

A spreader-sticker in a spray solution is designed to enhance the coverage of the chemical on the plant surface. By doing so, it helps ensure that the active ingredients adhere more effectively to the foliage, which is especially important for achieving thorough and even application. These substances improve the ability of the solution to resist being washed off by rain or irrigation, thereby increasing the effectiveness and longevity of the treatment.

The other options do not accurately describe the function of a spreader-sticker. While they imply useful effects, they miss the primary function, which is about enhancing adhesion and coverage, making option A the most relevant choice.