Question

Why is the axis of action also called the 180-degree system?

a. there are 180 degrees of space on the chosen side of the axis of action in which the camera may be placed to preserve screen direction.
b. there are 180 degrees of space on the chosen side of the axis of action in which the characters may move before they are offscreen.
c. the axis of action forms a 180 degree angle with the camera.
d. the axis of action forms a 180 degree angle with the actors?

Answer 1

The answer is:

a. there are 180 degrees of space on the chosen side of the axis of action in which the camera may be placed to preserve screen direction.

The camera must not cross the imaginary axis line to avoid creating a "reverse angle". Simply saying, the camera must only shoot on one side of the scene.