Concept:Visual aids are learning tools that rely on sight, like images, charts, or written words.
Explanation:Option A includes chalk, blackboard, and duster. Teachers use these to write and show visual information, so they are visual aids.
Option B has flash cards and charts. Both display pictures or text visually, making them clear visual aids.
Option C contains a projector, radio, audio tapes, and CDs. The projector can show visual content, but radio, audio tapes, and CDs deliver information through sound only. This mix includes auditory tools, so the whole set is not purely a visual aid.
Option D includes flashcards and a soft board. Flashcards are visual, and a soft board can hold visual displays like posters or diagrams.
Hence, the set that is not a visual aid is projector, radio, audio tapes, and CDs because it mainly involves hearing, not seeing.
Answer:C. Projector, radio and audio tapes and CDs