A projected aid uses equipment to display an image onto a screen or surface.
Why B fits: A blackboard is viewed directly after the teacher writes or draws on it; no image is projected.
Why the others differ: Overhead projectors, slide projectors, and epidiascopes use projection to display material.
Revision point: Projected and non-projected aids can both be useful. Choose an aid according to visibility, the lesson objective, and the material being taught.