Answer:
Option A, '“No, I am going to the library. Want to join me?”
Step-by-step explanation:
While sitting with friends, sometimes you have to do things which you don't want to do. But there are somethings that you think are not good to do. Such things are difficult to refuse while hanging out with friends. You cannot be rude to your friends and at the same time you cannot do what they want. So the best way to avoid such things is to direct the conversation towards a lighter mode.
So if your friends insist you to smoke, you can simply change the topic. In this case, you can simply imply that you are busy with studies and ask them to join as well.
If they don't want to come along, they will have to refuse putting the pressure on them!