Instructions: 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").
Input: If a species of plant or animal ceases to exist on earth, either by natural causes or by activities of humans, the loss of the plant or animal (A) reversible extinction (B) cannot be undone (C) reversible (D) a subspecies
Output:
B