Answer:
Talk to her brother and let her parents know if there is a problem.
Step-by-step explanation:
This is the statement that would most help Cynthia with this situation. In this example, it is obvious that the brother is trying to hide his actions. Therefore, he most likely is embarrassed or aware that he is doing something wrong. Therefore, Cynthia should first talk to him to figure out what he is thinking and feeling, especially because they have a good relationship. However, if any problem arises, she should talk to her parents.