Instructions: 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.
Input: Many cars today are designed to get better gas mileage than those made in the past. This change resulted from a need to  
 (A) recycle materials (B) improve safety (C) produce chemicals (D) conserve resources
Output:
D