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]: Ella waves good-bye from the bus. What body system pulls on bones to let Ella wave her arm?  
 (A) muscular system (B) nervous system (C) digestive system (D) circulatory system
[A]: A


[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 external stimulus causes a plant to bend toward it?  
 (A) a light source (B) a magnetic field (C) a spray of water (D) a source of wind
[A]:
A