Which of the following best provides evidence that there is a nuclear strong force?

Scientists have seen that protons and neutrons are electrically attracted to each other. This is a very strong force.
Scientists have seen that multiple protons that close together exert very strong electrical forces. There must be a very strong force to hold them together.
Scientists can pull on individual nucleons, and feel the resistance. This resistance is caused by the strong force.
Scientists have observed that neutrons have a very sticky surface. This "stickiness" produces a strong force.

Question

Which of the following best provides evidence that there is a nuclear strong force?
 	
   Scientists have seen that protons and neutrons are electrically attracted to each other. This is a very strong force.
Scientists have seen that multiple protons that close together exert very strong electrical forces. There must be a very strong force to hold them together.
	Scientists can pull on individual nucleons, and feel the resistance. This resistance is caused by the strong force.
	Scientists have observed that neutrons have a very sticky surface. This "stickiness" produces a strong force.

anonymous · Answer

Scientists have seen that protons and neutrons are electrically attracted to each other. This is a very strong force.