You will be given a definition of a task first, then some input of the task.
In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: Most invertebrates have a more complex nervous system., Fact2: Invertebrates are animals without a backbone., Question: what mostly have a more complex nervous system? (A) nerve cells (B) protist (C) animals without backbone (D) remains of prehistoric life (E) members of their own species (F) sensory neurons (G) Veins and arteries. (H) bacteria
Output:
C