Q: You are given a science question (easy-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.
What happens to metal railroad tracks during the heat of a summer day?  
 (A) decrease in weight (B) increase in weight (C) decrease in length (D) increase in length
A:
D