关于玛雅数系中“0”的说法正确的是(    )

   “Cool”is a word with many meanings．Its old meaning is used to express a temperature that is a little bit cold．As the world has changed，the word has had many different meanings． 
   “Cool”can be used to express feelings of interest in almost anything．
   When you see a famous car in the street，maybe you will say，“It's cool．”You may think，“He's so cool，”when you see your favourite footballer． 
   We all maximize（扩大） the meaning of“cool”．You can use it instead of many words such as “new” or “surprising”．Here's an interesting story we can use to show the way the word is used．A teacher asked her students to write about the waterfall（瀑布）they had visited．On one student's paper was Just the one sentence，“It's so cool．Maybe he thought it was the best way to show what he saw and felt． 
   But the story also shows a scarcity（缺乏）of words．Without “cool”，some people have no words to show the same meaning．So it is quite important to keep some credibility（可信性）．Can you think of many other words that make your life as colourful as the word “cool”？ I can．And I think they are also very cool．

我们知道三角形的内角和是180°，四边形的内角和可以转化成两个三角形的内角和来得到是360°，那十二边形的内角和是____°．