Answer:
A. Say no directly, with a "hands-off" gesture.
Step-by-step explanation:
Say no with a hands-off gesture is the best way to act if you don't want to participate in whatever they are offering you. This gesture express a firm and decisive stand towards their pressure, they will find you decided without any possibilities of changing your mind.
On the other hand, if you express doubt, shrugging your shoulders, showing indecision, showing funny gestures, they will just insist until you say yes, because your body language is saying "I don't know" or "I want to", which will offer to them a chance to convince you.