Jeanette was conducting an experiment to determine if plants grow better when exposed to rap music. She bought two identical plants and exposed one to rap music for two weeks while the other grew without music. From the data, Jeanette determined that plants do not grow better with rap music. Which of these would explain why Jeanette's conclusion may not be valid?
A) There was no control group.
B) She never formulated a question.
C) The experiment could never be repeated.
D) She should have tested more than two plants.