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

A dog's ears may be as thin as its (A) friend's (B) neighbor's (C) father's (D) owner's
C

Which is a producer? (A) cloudy mornings (B) vinyl (C) team Alicia (D) strawberries

D