All of the following are three-dimensional AV aids, EXCEPT:

Correct option is C

Charts are two-dimensional visual aids, whereas models, puppets, and specimens are three-dimensional. Charts are typically flat and do not have depth, making them different from the other options that involve tangible, three-dimensional items.
Explanation of options: (a) ✔ Models – Three-dimensional objects used to represent something in a scaled form. (b) ✔ Puppets – Three-dimensional objects that can be manipulated for educational purposes. (c) ✘ Charts – Two-dimensional visual aids, not considered three-dimensional. (d) ✔ Specimens – Three-dimensional objects, typically biological, used for study or display.