proof that light is a transverse wave lays in the fact that it
a. can diffract
b. slows down and bends toward the normal when it travels through a denser medium
c. travels though space, a vacuum
d. can be polarized
e. can disperse when shone through a glass prism at the right angle
d. can be polarized.
Only transverse waves can be polarized, meaning their electric and magnetic fields oscillate perpendicular to the direction of propagation. Light can be polarized, providing evidence that it is a transverse wave.