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: cold fronts cause thunderstorms as they pass by, Fact2: If cold air replaces warm air, it is called a cold front., Question: What does cold air replacing warm air cause? (A) Greenhouse gases (B) Pollution (C) Dehydration (D) thunderstorms (E) steady barometer readings (F) hypothyroidism (G) constant air pressure (H) stagnant air temperature
A:
D