Answer: A) Don't be jealous
Step-by-step explanation:
According to the question,Sandy is mad at Kim because she has started dating a boy and now has a boyfriend but Sandy does not have boyfriend .Thus ,Sandy has stopped talking to Kim as she is feeling jealous of her friend .Thus, she is breaking rule of not being jealous of your friend rather support and feel happy for him/her.
Other options are incorrect because standing up for friend,volunteering when friend is in need and oblige for giving complement and repaying favors are not the rules of friendship broken by Sandy.Thus, the correct option is option(A).