Complete the summary by choosing one sentence (A,...

Câu hỏi: Complete the summary by choosing one sentence (A, B, C, or D) that is among the most important ideas in the passage in the blank.

A Because a blue moon is uncommon, “once in a blue moon” means “rarely” or “never”. 

B The calendar devised by the Romans works well .

C The lunar calendar was invested by Julius Caesar and Augustus Caesar. 

D The Roman calendar is still in use today.