Given the task definition and input, reply with output. 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").

From 2008 to 2018, the concentration of single carbon molecules bonded with two oxygen molecules present in the air has dramatically (A) sharply declined (B) grown (C) decreased (D) polluted public opinion
B