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.

[Q]: Which of these elements is found in the greatest amount in organisms?  
 (A) carbon (B) iron (C) lead (D) neon
[A]: A


[Q]: Which type of organism is at the lowest level of the food chain?  
 (A) autotroph (B) heterotroph (C) carnivore (D) omnivore
[A]: A


[Q]: When the pesticide DDT was first used, it killed nearly every mosquito it touched. Within a few years, however, many mosquitoes became resistant to DDT and survived. What enabled this to happen?  
 (A) meiosis (B) migration (C) immune responses (D) gene mutations
[A]:
D