In the fishbowl, the glass, water, rocks, and plastic plants are in thermal equilibrium. this situation means the temperature of the rocks is ° f. nextreset

The temperature of the rocks is just equal to the temperature of the glass, water and plastic plants for they are in thermal equilibrium. The thermal energy present in that environment transfers from one thing to another, resulting to having the same temperature among the objects inside the fishbowl. Therefore, if the temperature of the glass is 75 degrees then the rest of the object will have the same temperature as they are in thermal equilibrium. 

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."