The reaction of Grignard reagents with aldehydes (such as methanal) leads to the formation of alcohols after hydrolysis. In this case, CH\(_2\)OH is an alcohol, and the correct Grignard reagent for methanal would be a methyl group (CH\(_3\)-) attached to magnesium bromide (MgBr).
Therefore, the correct answer is MgBr (option D), which reacts with methanol to form CH\(_2\)OH.