You decide to make yourself a desk, by attaching a wide shelf to the top of two legs. (A side view is shown.)

When you put a book down on the end of the shelf, the force exerted ON the shelf

at the attachment point labelled "A" is approximately

BLUE: Upwards

YELLOW: Downwards

GREEN: Rightwards

PURPLE: Leftwards

PINK: Zero

(Same question for attachment point "B")