(列方程解答)一艘船从甲码头到乙码头顺流行驶，用了2小时；从乙码头返回甲码头逆流行驶，用了2.5小时．已知水流的速度是3千米/时，求船在静水中的平均速度．
解：设船在静水的平均速度为x千米/时，根据题意，得（1分）
2（x＋3）＝2.5（x－3） （4分）
解得 x＝27 （6分）
答：船在静水的平均速度为27千米/时．（7分）
等量关系为：顺水速度×顺水时间=逆水速度×逆水时间．即：2×（静水速度+水流速度）=2.5×（静水速度-水流速度）．
| 完形填空。 | |||
| It`s fourteen years since I left the Philippines to live with my family in the USA. A month ago, while on summer vacation back in my motherland, I learned a lesson from mosquito bites. Right before __1__ Kennedy Airport in New York, my grandmother __2__ me of the behaviour of the native mosquitoes around the __3__ like me. She said. “There`s an old saying---the __4__ you stay away from the motherland, the sweeter you blood __5__ to the mosquitoes.” Not __6__ it, I replied, “ Grandma, that`s just an old wives` tale!” Well, less than a week after my arrival in Manila, I was already carpeted with a ___7__ of mosquito bites. I took many measures to keep myself from being __8__, but they all proved useless. Late one night in my cousin`s home, I couldn`t bear the __9__ of the bites. Hoping to find some comfort, I __10__ my cousin, who was sleeping peacefully in the bed next to mine. Unhappy for being __11__, she said, “ There is nothing you can do. Go back to sleep.” With a few turns, she slept again. Enviously(嫉妒地) watching her sleep, I hoped a big mosquito would __12__ on her face. However, the mosquitoes would just lightly danced around her forehead and fly away quickly, never biting her. Amazed, I ran to others` rooms, only to find they were all sleeping __13__ as the same thing occurred again and again. From those bites, I came to __14__ my grandma`s silly tale. From then on, I`ve always tried to keep a(an) __15__ mind about those strange old wives` tales because they do have truth to them. | |||
| （ ）1. A. leaving （ ）2. A. persuaded （ ）3. A. students （ ）4. A. earlier （ ）5. A. grows （ ）6. A. expecting （ ）7. A. shade （ ）8. A. touched （ ）9. A. noise （ ）10. A. woke up （ ）11. A. blamed （ ）12. A. land （ ）13. A. joyfully （ ）14. A. tell （ ）15. A. open | B. passing B. reminded B. friends B. longer B. goes B. understanding B. pile B. bitten B. hit B. shouted at B. interrupted B. fly B. anxiously B. know B. active | C. visiting C. warned C. passengers C. sooner C. flows C. recognizing C. cloud C. defeated C. pain C. looked at C.moved C. fall C. soundlessly C. remember C. clear | D. finding D. informed D. visitors D. later D. remains D. believing D. blanket D. discovered D. effect D. dropped on D. frightened D. wait D. worriedly D. accept D. honest |