What Purpose Does Positive Beam Limitation Serve

What purpose does positive beam limitation serve?

A) To prevent the technologist from placing an image receptor in the Bucky tray that is too large for the study performed
B) To allow the technologist to use an exposure field larger than the image receptor size
C) To prevent first-year students from having to repeat studies by not aligning the Bucky tray with the image receptor
D) To reduce patient exposure by limiting the exposure field to the same size as the image receptor in the Bucky tray