Answer:
C. Stopping a friend from plagiarizing a paper
Step-by-step explanation:
First, to answer the question, you must define bystanders. A bystander is a person who is present at an event but does not take part in it. So a positive bystander would be a person who prevents another person from making a bad decision. Therefore, C would be correct because in that answer the bystander is stopping a friend from breaking the rules.