It looks like you're asking about the definition of prehistory and its characteristics. Prehistory is indeed the period of time before written records existed, which means it encompasses the development of human culture and societies prior to the advent of writing systems.
To clarify your points:
A. People left written records - This is not part of prehistory. Written records begin with the historical period. Prehistory is defined by the absence of written documentation.
B. People created calendars - While early forms of tracking time existed (like lunar calendars), these developments occurred in the prehistoric era, but calendars are not a definitive characteristic of prehistory itself.
C. People began to study history - The study of history typically refers to periods after written records began. Prehistory refers to all the time before that, which is studied primarily through archaeology and anthropology rather than written history.
In summary, prehistory refers to the era before written documentation, encompassing the origins and development of early human societies and cultures. Would you like to know more about a specific aspect of prehistory?