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: Differentiation is the process by which unspecialized cells become specialized., Fact2: Methods and processes are activities., Question: What is the method by which unspecialized cells become specialized? (A) Laboratory (B) Pasteurization (C) pigmentation (D) Differentiation (E) several genes (F) polygenic trait (G) prokaryotic cells (H) chondrocytes
A:
D