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").
Q: Fact1: Biodiversity increases the productivity and stability of ecosystems., Fact2: Biodiversity and ecosystems are complex systems., Question: What type of system is biodiversity? (A) our planet (B) insects (C) good (D) complex (E) trees (F) animals (G) fertile (H) vegetation
A:
D