We have two possible answers: acid rain and floods. We will analyze both to see which is correct.
Floods happen when level of water increases. This most often happens after big rain has fallen or when the ice starts to melt. This also most often happens close to rivers. Does it matter where does this extra water come from? No, it does not matter. Rain created in any type of atmosphere and snow melted in any mountain can create floods.
Acid rain got it's name because it is more accidic than normal rain. Rain is created of small droplets of water. Water gets acid when some chemicals are dissolved. These chemicals are most often compounds of a sulphur. Sulphur compounds can be found in exhaust gases of a car. Best source of all chemicals that create acid rain is a smog.
Correct answer is: A. acid rain