Students in Dr. Branch's physics class were calculating the average time required for one complete period of a pendulum bob. They set up five pendulums and timed the swing for each one twenty-five times. Then they calculated the average period time One set of data varied significantly from the other sets. What could be one source of unavoidable error that influenced the data?

A) reading the stop watch incorrectly

B) stop watch starts with one second on the clock

C) not starting the timer at exactly the “go” call

D) students not paying attention to data collection