“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．

生活中，我们都希望拥有美好的情感。下列关于美好情感的产生，认识正确的是（    ）

如图，O为坐标原点，四边形OABC为矩形，A（10，0），C（0，8），点P在边BC上以每秒1个单位长的速度由点C向点B运动，同时点Q在边AB上以每秒a个单位长的速度由点A向点B运动，运动时间为t秒（t＞0）．

（1）若反比例函数y=$\frac{m}{x}$图象经过P点、Q点，求a的值；

（2）若OQ垂直平分AP，求a的值；

（3）当Q点运动到AB中点时，是否存在a使△OPQ为直角三角形？若存在，求出a的值，若不存在请说明理由；

在雅安地震中，小明受伤了需要输血，小明的爸爸（A型血）、小明的妈妈（B型血）和已经年满18岁的哥哥（O型血）都想给小明献血，但医生说，三人中只有爸爸的血绝对不能输给小明，小明的血型是（　　）