One of the following is an example of a variable duration foreperiod

One of the following is an example of a variable duration foreperiod: Group of answer choices A swimmer during practice used 5 second periods between the onset of the warning signal and the firing of the starter gun A sprinter improving his anticipation skills by practicing the addition of variable times between the beginning of the warning signal and the firing of the starter gun with some catch trials A baseball player used a pitching machine that fires a ball every 10 seconds All of the above are examples of using variable duration Foreperiods