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.

Example Input: What unit of measurement would be used to describe the melting point of a substance?  
 (A) liters (B) grams (C) degrees (D) centimeters
Example Output: C

Example Input: A brand of fertilizer claims that it contains all the chemicals a plant needs for rapid growth. It may be inferred that the fertilizer includes all these ingredients except  
 (A) potassium. (B) phosphorus. (C) carbohydrates. (D) nitrogen.
Example Output: C

Example Input: In what way can bacteria be good for the human body?  
 (A) Bacteria help the body have strong bones. (B) Bacteria help maintain body temperature. (C) Bacteria help deliver oxygen to the cells. (D) Bacteria help break down food.
Example Output:
D