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. 

[Q]: Coal is loaded into the firebox. The boiler produces steam under high pressure. The steam generated in the boiler flows down into a cylinder. Just ahead of the wheels, pushing a tight-fitting plunger, the piston. The piston is connected to one or more of the locomotive's wheels through a kind of arm-elbow-shoulder joint called a crank and connecting rod. As the piston pushes, the crank and connecting rod turn the locomotive's wheels and power the train along. An outlet valve opens and the piston pushes the steam back through the cylinder and out up the locomotive's chimney. 
[A]: coal ,steam 


[Q]: You take some paper. The writing tools. You write a message describing what's on your mind. You put the letter into an envelope. You take the letter to the post office. Send it to its recipient. 
[A]: paper ,writing tool ,message ,letter 


[Q]: 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. 
[A]:
light ,small image ,retina's rods and cones ,electrical pulses