mrs. rodrigues wants to compare the spread of the test scores of her two biology classes. which statistic should she use? (multiple choice)

a.) mean
b.) standard deviation
c.) median
d.) mode

if anybody can help me with this, thank you so much! i'm trying to pass a pre-test on e.d.g.e.n.u.i.t.y :( if you know the answer, please explain instead of just giving me the answer alone. thank you! <3