TASK DEFINITION: In this task, you are given a paragraph, and your job is to generate comma-separated entities present in the given paragraph. Generate entities from a given passage in such a way that (i) they are present in the paragraph, (ii) they are non-duplicate, (iii) they underwent a state change during the process. Avoid creating entities that (i) aren't present in the process paragraph and (ii) aren't significant. 
PROBLEM: Electrical signals in the brain travel through nerves to muscles. Two types of proteins exist in filaments in the muscles. The filaments move when the brain instructs them to. The motion of the filaments cause the muscle to shorten and contract. Opposing pairs of muscles exist in order to provide the necessary range of motion. 

SOLUTION: electrical signals ,proteins ,filaments 

PROBLEM: The cornea and lens refract light into a small image. Shine it on the retina. The retina's rods and cones convert it to electrical pulses. The optic nerve carries electrical pulses through the optic canal. Nerve fibers end in the lateral geniculate nucleus and the visual cortex. 

SOLUTION: light ,small image ,retina's rods and cones ,electrical pulses 

PROBLEM: Several types of gases form in the atmosphere. May come from different sources. The gases remain trapped in the atmosphere. Through the suns light the gases hold in heat and energy. Trap them in our atmosphere. The earth may become warmer this way. 

SOLUTION:
several types of gases ,atmosphere ,earth ,heat ,energy