A simple pendulum is made by attaching a mass to the end of a string and allowing the mass to swing back and forth. The "period" of a pendulum is the amount of time it takes the mass to complete one swing.

(You do NOT need to have studied pendulums in class to answer this question correctly.)

A student wants to find out if the period of a pendulum depends on the mass of the swinging object or the length of the string or both. She wants to design an experiment to see if the length of the string of the pendulum will affect the period of the pendulum. Of the following sets of trials listed below, which set will allow the student to tell if the length of the string affects the period of the pendulum assuming the period of the pendulum is measured accurately?

a.

Trial	Mass	Length	Period
1	100 g	75 cm
2	100 g	75 cm
3	100 g	75 cm
4	100 g	75 cm

b.

Trial	Mass	Length	Period
1	100 g	25 cm
2	100 g	50 cm
3	100 g	75 cm
4	100 g	100 cm

c.

Trial	Mass	Length	Period
1	50 g	75 cm
2	100 g	75cm
3	150 g	75 cm
4	200 g	75 cm

d.

Trial	Mass	Length	Period
1	50 g	25 cm
2	100 g	50cm
3	150 g	75 cm
4	200 g	100 cm

e.

[None of the above.]