In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").

the presence of which of these is required for the formation of cavernous chambers? (A) some carbonated soda (B) some carbon dioxide (C) some carbonic acid (D) carbon monoxide gas
C

Though fossil fuels and their byproducts will eventually be used up completely, we'll still have (A) gasoline (B) coal (C) plastics (D) light from stars
D

There are now many more people because of (A) efficient farming (B) more cities (C) computers (D) global warming

A

