What are the gender symbols on the bathroom doors at school and other illustrated symbols that stand for some concept called?

The correct answer is C. pictographs.

Pictographs are visual symbols that represent specific concepts or ideas, such as gender. The symbols on bathroom doors (often depicting male and female figures) are a good example of pictographs since they convey information without the use of words. They help people quickly identify the purpose of the space. If you have more questions or need further assistance, feel free to ask!