Occasionally, a Feature Movie Will Be Shown on Television with Black

Occasionally, a feature movie will be shown on television with black bars at the top and the bottom of the screen. Why is this done?

A) to show the entire aspect ratio of the wide-screen movie on the standard TV screen
B) to make sure the credits can be read
C) to focus viewer attention within the essential area
D) to convey that the program we are watching was originally filmed
E) to enable the use of computer graphics in the movie