Equilibrium is reached when the net reaction is zero. The reaction is consistent, when reactants and products are neither excessively consumed, nor produced.
The rate of the forward reaction is equal to the rate of the reverse reaction.
Answer:
I'd say "a" because not everything with plants and animals is perfectly organized together nothing ever is.
B, the height above or below sea level
I would say C is the most correct.
In D it depends on what water source you're using. Let's say it is a waterfall, then the source of the water (melting ice or a lake) may disappear in the future.
If you're using underwater "windmills" placed in the ocean, then you would expect it to last a while as the ocean will not disappear in the near future.
