78. Fill in the blank in Paragraph 5 with proper words. (within 5 words)

77. Which sentence in the text is the closest in meaning to the following one?

Teachers and students got friendlier so that the students became more active in learning and scored higher in tests.

____________________________________________________________________________

76. What does the author say about the adults according to Paragraph 1? (within 8 words)

_________________________________________________________________________

5] So maybe we can make the world a better place by____________. After a month of doing it. I feel lighter and more connected and I have a better sense of well-being.　

4] It’s a form of universal health insurance. It’s impossible to say hello without smiling. And smiling has been shown to lower blood pressure, relieve stress and boost happiness. Apparently, a smile creates a similar effect in the recipient (接受者)。

3] Environments influence friendliness, One study found that people in the city were kiss likely to one hands with a stranger than those in the countryside. And researchers say, pleasure environments generally encourage more smiles and hellos than unpleasant ones. My experience was similarly. Whatever the reason, my urban hellos were answered far less often than my rural one. Similarly, people in vacation spots, like the Jersey Shore, were far friendlier than those hurrying work downtown.　

1] Hello. It’s one of the first words we learn as babies, yet it’s one of the last ones we think to use as adults. That’s unfortunate, because saying hello is more than just saying hello-it is recognition of another’s worth. How might the world change-how might we change-if we mastered this word? To find out, I spent one month saying hello to every person I met. Here’s what I’ve learned.

　[2] It can boost(促进)productivity. In one of the few studies ever done on this subject, Allan Allday, an assistant professor of special education at Oklahoma State University, had middle school teachers greet their students individually each morning. This exchange of greetings raised the kids’ productivity. School went from impersonal to personal, and that resulted in more class participation and better grades.

21.(本小题满分14分)设数列的前项和为，已知，，，且，，其中、为常数．

(Ⅰ) 求与的值；

(Ⅱ) 证明数列为等差数列；

(Ⅲ) 证明不等式对任何正整数、都成立．

2009-2010学年度第一学期

20. (本小题满分14分)在平面直角坐标系中，已知圆的圆心为，过点且斜率为的直线与圆相交于不同的两点,．

(1)求的取值范围；

(2)是否存在常数，使得向量与共线？如果存在，求值；如果不存在，请说明理由．