In an experiment to determine the acceleration due to gravity, one student holds a pencil at arms length and drop it. another student starts a timer when the first student lets go and stops the timer when the pencil hits the ground. they repeat this several times and takes an average. is this a valid experiment, why or why not? a. no, it is not valid because they are only dropping one item. b. no, it is not valid because taking the average will increase rounding error. c. no, it is not valid because the short distance means there will be a lot of error due to the students reaction time. d. yes it is valid