Answer:
B. Marc, who just joined a new school and is finding it hard to make friends, especially because his parents are away a lot.
Step-by-step explanation:
Marc is most likely to give into peer pressure because his tendency to please his friends is higher compared to Katrina and Becky. The fact that Marc's parents are not present most of the time to guide him or give him an advice will make him at a higher risk to fall prey to peer pressure.
Once Marc finds a set of friends, he'll be encouraged to conform/adapt to their rules in order to keep the relationship. This means that even if his friends will use illegal drugs, Mark has a high probability to follow them. This is also because he doesn't have anyone to confirm whether his actions are good or not because his parents are away and he doesn't want to be lonely in the new school.