An electromagnetic wave is traveling in a vacuum. The magnitudes of the electric and magnetic fields of the wave are ______, and the electric and magnetic energies carried by the wave are ______.
(a) Equal, proportional (but not equal) to each other
(b) Proportional (but not equal) to each other, equal
(c) Equal, equal
(d) Proportional (but not equal) to each other, unequal