1-C. The base-60 system did not appear in human history until recently.The base-60 system did not appear in human history until recently.
60進法は、現れなかった、人類の歴史にダヨ、最近までダヨ。
2-C. Ancient Mesopotamians believed the base-60 system was unusual.Ancient Mesopotamians believed the base-60 system was unusual.
古代のメソポタミア人は、信じていた、60進法が普通でなかった(時制の一致)とダヨ。
3-C. In paragraph (2,) the author tells us that the base-60 system is highly convenient for measuring time .In paragraph (2,) the author tells us that the base-60 system is highly convenient for measuring time .
4-C. The Mesopotamian year was divided into 360 days, so the base-60 system fit very well into their calendar.The Mesopotamian year was divided into 360 days, so the base-60 system fit very well into their calendar.
5-C. Ancient Mesopotamians, whose system of time we have adopted, are believed to have used a base-60 system.Ancient Mesopotamians, whose system of time we have adopted, are believed to have used a base-60 system.