Please choose the correct answer to the question: Four students are investigating the effect of the force of a baseball bat on a ball. They marked the four different points where each of the balls made contact on the bat after each strike by each of the four students. Which of the following describes an error in the experimental design?

Answer1: failure to conduct enough trials Answer2: not considering the spin of the ball Answer3: not using balls of different masses Answer4: failure to define one testable variable

Answer format: answer1/answer2/answer3/answer4