A homeowner put a brand-name fertilizer/weed killer on half of his lawn and a generic fertilizer/weed killer on the other half. After three weeks, the generic side had 1 weed per square meter, the other side 1.7 weeds per square meter. The generic side required two mowings in the 3 weeks, the brand-name side one. The homeowner concluded that the generic was superior to the brand-name. Determine which evaluation guideline applies best in questioning the results of the described study.

A. Consider possible confounding variables.

B. Consider the sample.

C. Consider the type of study.

D. Consider the source.