如果a和b都是非零自然数，并且满足
|
+a 4
=b 7
可变形为：7a+4b=27，即b=27 28
，27-7a 4
因为a和b都是非零的自然数，所以a＞0，7a＜27，
即0＜a＜
，那么a是1，2，3，27 7
则a=1时，b=5，
a+b=1+5=6；
a=2时，b=
（不合题意舍去）；13 4
a=3时，b=1.5（不合题意舍去）．
故a+b=6．
故答案为：6．
| 完形填空。 | |||
| Zhang Jin was excited to get the prize of a free trip to Thailand from his company. But the manager from Qingdao, Shandong Province, didn't expect 1 a dangerous experience. The next day, upon Zhang's arrival in Bangkok, the capital of Thailand, he was _2 to find himself in a city filled with street fights 3 two groups. One group was supporting the Thai government while 4 was against it. The anti-government group has taken 5 actions recently. It took over the prime minister's ( * * ) office in August and they had street fights _6 _ the police. Two people were reported to __7 and hundreds injured. Last month the anti-government group took over two international airports in Bangkok and stopped all 8 . About 240,000 foreign tourists, 9 over 3,000 Chinese people like Zhang had to stay in the country. "We were nervous on the streets. But we felt safe at home with other Chinese from Hong Kong or Taiwan," said Zhang. Luckily, the Chinese government sent special flights to 10 the people back. Now, all the Chinese tourists are safely back home. "The moment the plane left Thailand, we cheered for joy, "said Zhang. | |||
| ( )1. A. has ( )2. A. surprised ( )3. A. among ( )4. A. another ( )5. A. quite a few ( )6. A. to ( )7. A. kill ( )8. A. ships ( )9. A. except ( )10. A. take | B. to win B. surprise B. in B. the other B. no B. about B. be killing B. flights B. but B. bring | C. to have C. surprising C. with C. other C. much C. with C. killing C. trains C. including C. send | D. win D. surprises D. between D. others D. few D. for D. be killed D. buses D. besides D. come |