instruction:
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. 
question:
Water flows by rocks. Chemicals are in the waters. Chemicals react with rocks. Rocks change to a different kind of rock. Oxygen in the air reacts with rocks. Rocks change to a different kind of rock. 
answer:
water ,rocks ,chemicals ,oxygen 


question:
Stars burn mass. The star burns until it runs out of fuel. The star can no longer support its weight. The layers of hydrogen press down on the core. The core gets smaller and smaller under the pressure. The pressure causes gravity to get stronger. The gravity becomes so powerful that nothing can escape it. Anything that gets close to it, is drawn into it by its gravity. Light is drawn into it. Light can not escape. 
answer:
Mass ,Fuel ,Gravity 


question:
Solar panels are made up of two types of silicon. Sun shines on solar panels. Sunlight goes into the top half of the solar panel. Sunlight travels into the bottom half of the solar panel. The "jump" between the two halves can be used to make direct current. A solar "inverter" changes the direct current to alternating current. Alternating current can be used to power things in your house. 
answer:

sunlight ,direct current ,alternating current