①用凉开水漱口

②在载玻片中央滴一滴生理盐水

③盖盖玻片

④染色

⑤取口腔上皮细胞,并将有口腔上皮细胞的牙签在载玻片的生理盐水滴中涂抹几下

⑥擦载玻片和盖玻片

    Bill is only fifteen years old，but he's already very rich．Two years ago，Bill began a football website（网站）for young people. "I became interested in computers when I was 8 years old  because my father's job is with computers．As a little boy，I also loved football and so I decided to make a website，especially for people of my age．"

    Bill started the "Football OK!" website two years ago，and now more than 20,000 people visit it every day．

    Bill is a schoolboy and a businessman as well．He usually gets up at six o'clock and looks at his e-mails．Then he goes to school from nine to four．In the evenings，he always works for about four hours on his website．

    Bill's next plan is a new website." At the moment I am thinking about a new website on American football，maybe for next year．"

    And is Bill the same person that he was three years ago? "'No，I am very different now．I have met a lot of interesting people on the website and I have traveled all over the world．" Bill doesn't know about the future．"Maybe I will sell the websites. I really don't know．I'll just wait and see."

    Some people say that when he is 21，Bill will be a millionaire（百万富翁). He always says, “Anything is possible”!

化简：$\frac{a-b}{a+b}$÷（a﹣b）•$\frac{1}{a-b}$=　　____ ；计算：$\frac{m+2n}{n-m}$+$\frac{n}{m-n}$﹣$\frac{2m}{n-m}$=____