You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Q: Cell differentiation is the result of gene expression. Genes can be regulated several ways. For example, small interference RNA molecules (siRNA), prevent gene expression by binding to the product of transcription. How do siRNA molecules silence genes?
(A) They bind to ribosomes. (B) They bind to tRNA. (C) They bind to RNA polymerase. (D) They bind to mRNA.
A:
D