Question

which best identifies a key characteristic of a manual?

diagrams and other media

cited research materials

a section for definitions

wordy explanations

Answer 1

If you are referring to the manual as in the instruction book, then the 2nd and 3rd options are eliminated. Out of options 1 and 4, the 1st option works best, so I would say that the correct answer is 
Diagrams and other media.

Answer 2

The option that best identifies a key characteristic of a manual is a section for definitions.

A manual is a technical document, that explains the steps to operate a device. It is very important to know the target audience to make it user-friendly, brief by getting to the point and detailed but not so much that is overloaded with useless information. A glossary of important terms should be included.