The visible spectrum refers to the

a. portion of the whole spectrum of light that is visible to the human eye.
b. effect of intensity on how we see dark to grey to white.
c. effect of the sound density on the perceptions of those with synesthesia.
d. well-known fact that colors are less visible to some men's eyes.
e. radiation waves that fall between 20 and 20,000 hz.

a. portion of the whole spectrum of light that is visible to the human eye.