Answer:
False
Explanation: sound travels fastest through solids slowest through liquids.
The correct answer is A. Mitochondria is the one that is responsible for everything that has to do with energy.
For a closed system, you need two things:
1) a conservation of mass within the boundaries of the system
2) the ability to freely exchange energy to & from the "closed" system with a surrounding external system
So, the answer is <u><em>never</em></u>, since your defining the "system" as the water within the bathtub, and an open bathtub is exposed to evaporation, which is not conserving mass within the defined "system".
I would agree with the second one, not the first. You can't always see the chemical reaction, and it isn't always sudden. But the second claim is true.