In Piaget's Swinging Pendulum Experiment, What Strategies Did Adolescents in Formal

In Piaget's swinging pendulum experiment, what strategies did adolescents in formal operational thought use?

A) They randomly changed variables so could not come to clear conclusions
B) They changed one variable at a time and therefore could come to a conclusion
C) They could not decide on a strategy to use to solve the pendulum problem as it was too complex
D) They made the pendulum too heavy so that it slowed down