Final answer:
The correct answer is C. Native Slavic inscriptions from the pre-Christian era.
Step-by-step explanation:
The correct answer is C. Native Slavic inscriptions from the pre-Christian era.
Descriptions by Roman historians, accounts by travelers from the Middle East, and writings by Byzantine missionaries and their successors are all existent sources of knowledge for early Slavic history. These sources provide valuable information about the interactions and cultural exchange between the Slavic people and other civilizations during that time.
However, native Slavic inscriptions from the pre-Christian era are not an existent source of knowledge for early Slavic history. This is because the Slavic people did not have a writing system during that period, and their history and culture were primarily transmitted orally.