Teacher: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.
Teacher: Now, understand the problem? Solve this instance: A farmer wants to know if adding fertilizer to his field will make his crops healthier. Which activity should the farmer do first?  
 (A) Plant different crops in a nearby fertilized field. (B) Water the crops in the field before adding fertilizers. (C) Add many different fertilizers to the field at once. (D) Record the appearance of the crops before fertilizing.
Student:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
D