The correct answer is option A. Marty's friend counterclaim is appropriate because it is both defensible and arguable. A counterclaim is a response to the claim, with the objective of rebutting the statement that was made in the claim. Marty's friend counterclaim, stating that nutrition education has no effect on obesity, is an acceptable counterclaim because it is capable of being defended and but is also arguable, meaning that it is not certain or clearly true, it is open for debate.