Final answer:
The primary function of informative presentations is to educate or inform the audience, often supported by various types of media.
Step-by-step explanation:
One of the primary functions of informative presentations is c) To educate or inform the audience. An informative speech aims to provide valuable information that is clear and comprehendible to the listeners. This type of speech includes various methods such as explaining a concept, describing an object, or demonstrating a process - for instance, how to change a tire or operate a thermostat. During an informative speech, speakers often use supporting media like visuals, video, or physical objects to help convey their message effectively.