Answer:
Set aside a sum of money that he will only be allowed to spend if he achieves the desired grade for the class. ⇒ REWARD
Rewarding himself with some type of treat only after he has studied. ⇒ REWARD
Step-by-step explanation:
Your friend could use conditional training to change his behavior. But which is more efficient, punishments or rewards? Generally, most people consider that rewards are more efficient than punishments. Doing something because you can gain something good from it is better than not doing something because you are afraid of the punishment or the bad consequences.
Making a firm commitment to study with someone else can also yield a reward (social reward), the problem is that the option states that his partner depends on your friend for him/her to study. It is never good to depend on someone else to do something that you should be able to do for yourself. This means that both, your friend and his study partner, have serious issues regarding their study habits. Unlike math, two negatives do not form a positive in real life. The option would have been valid if your friend just committed himself to study with someone else.