“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．

下列四个地区，水循环最为活跃的是(   )

有这样一个两位数，个位上的数字和十位上的数字之和等于10。你知道这样的两位数有多少个吗?分别是多少?