Why is it important to use an ALT attribute within an image tag in an HTML document?

Why is it important to use an ALT attribute within an image tag in an HTML document?

A.
It allows for animated images to be displayed by making use of the primary image and the
image specified in the ALT attribute.

B.
It allows for an alternate image to be displayed if the primary image cannot be found.

C.
It allows for an alternate image to be displayed if the primary image is not displayable in the
requesting device.

D.
It allows for descriptive text to be displayed if the requesting device does not display inline
images.