C. He compares the colonies to pieces of a snake because he believes the colonies will be ineffective unless they work together.
His caption says "Join, or Die". This shows that Franklin feels that the colonies cannot survive if they are divided. A snake would not be able to divide if it was separated into different parts just as the colonies will not be able to survive if they do not work together. It would be easier for the British to keep their control if they only had to fight one colony at a time instead of all of them together working towards a common goal.