Assuming you had to choose between:
A. France
B. the Czech Republic
C. Switzerland
The answer is the Czech Republic (B) .
The Carolingian Empire ruled over western and (parts of) central Europe throughout the 9th century, after Charlemagne was named Emperor of the Romans by Pope Leo III in 800. Charlemagne's conquests did not cover the whole of today's Czech Republic, but did expand north of it into present-day Germany, and south of it into present-day Austria and Italy.