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]: Many things can contribute to the development of a theory. A student made a list of some things that might help scientists develop a theory. Observations Calculations Conversations Publications From the student's list, which must be used in the development of every theory?
(A) Observations (B) Conversations (C) Publications and calculations (D) Calculations and conversations
[A]: A

[Q]: A student has decided to investigate whether the number of flowers on a plant will increase if the water supply to the plant is increased. She has five pots of geranium plants to use in her experiment. What factor in the experiment should be varied for the five plants in order to answer the student's question?
(A) age of seedlings (B) temperature of water (C) volume of water (D) number of hours in sunlight
[A]:
C