Arie has come to understand that she has to study if she wants to pass her classes, but she also knows there will be times when her motivation to study will be very, very low.
what is the best way for her to make sure she continues to study through periods of low motivation?

by developing the habit of studying for each class, according to a schedule                                                              

Explanation:

           Motivation is the process by which people stimulate to action in order to accomplish their dreams and goals. It is the desire of people to get something or achieve something in life as a part of their goal.

           In the context, Arie wants to pass the exam and she knew that in order to pass the exam she needs to study hard. But Arie is also aware that at times she will be low in motivation to study. The most appropriate way to keep up the motivation in times of low motivation period is to develop the habit of studying hard for each classes according to the study schedule Arie has made to study. By this way she can study and maintain her motivation to pass the exam.