Given the task definition and input, reply with output. 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: high pressure systems cause clear weather, Fact2: Weather Clear weather usually means good visibility., Question: What causes good visibility? (A) permineralization (B) focusing a lens (C) high pressure systems (D) flashlights (E) peachleaf willow (F) the Great Barrier Reef (G) an electron microscope (H) windpower operated machines
C