The correct answer is C: Boxer blindly follows the rules of Animal Farm, while Clover silently questions some of Napoleon's decisions. Both Boxer and Clover are strong and loyal to the Revolution and their comrades on Animal Farm. Boxer's loyalty--coupled with the fact that he is not capable of deep thinking--causes him to accept the statements of the pigs without question. He truly cares about Animal Farm, and he helps it the best he can by doing what he does best: hard work (His motto is "I will work harder").
Clover--though loyal--secretly questions some of Napoleon's decisions. She recognizes the hypocrisy of the pigs--such as when the pigs begin sleeping in beds despite previously passing a law which forbade animals to sleep in beds--but she does not have the vocabulary or rhetorical skills to organize a resistance to the pigs' rule All she can do is watch as the pigs resort to the ultimate example of cruelty: murdering their fellow animals in cold blood. As Orwell describes:
As Clover looked down the hillside her eyes filled with tears. If she could have spoken her thoughts, it would have been to say that this was not what they had aimed at when they had set themselves years ago to work for the overthrow of the human race. These scenes of terror and slaughter were not what they had looked forward to on that night when old Major first stirred them to rebellion.