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").

[EX Q]: 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
[EX A]: C

[EX Q]: Where might you find the substance used to make the shiny metallic foil paper used in cooking? (A) Clouds (B) Rocks (C) Wood (D) Leaves
[EX A]: B

[EX Q]: Which likely increased atmospheric CO2 recently? (A) sustainable fisheries (B) electric cars (C) motorcycles (D) ant populations
[EX A]:
C