Final answer:
The correct answer to the student's question is 'a) Lunar, circle,' referring to the Sumerians' development of a lunar-based calendar and the division of a circle into 360 degrees.
Step-by-step explanation:
The student's question refers to the ancient inventors of calendars and the division of circles into degrees. The correct answer is: a) Lunar, circle. The Sumerians devised a calendar based on lunar months and divided the 24 hours of the day into 60 minutes with 60 seconds each. They also divided the circle into 360 degrees. Various ancient civilizations developed calendars based on the movements of celestial bodies to organize agricultural activities and religious rituals.