题目内容：

阅读下面材料，在空白处填入1个适当的单词或括号内单词的正确形式。

Dujiangyan was built over 2,200 years ago in what is now Sichuan Province in Southwest China. It is 1. oldest man-made water system in the world. This amazing engineering achievement is still used today to irrigate over 6,000 square kilometers of farmland, take away floodwater and provide water for fifty 2. (city) in the province.

In ancient times, the region in 3. Dujiangyan now stands suffered from regular floods 4. (cause) by the overflow from the Minjiang River. Li Bing, the governor of the region, together with his son, decided to find a way to solve the problem.

The simplest way was to build a dam, 5. this would ruin the Minjiang River. So Li designed a series of channels that would take away the floodwater while leaving the river flowing 6. (free). Better still, the extra water could be directed to the dry Chengdu Plain, making it 7. (suit) for farming.

Once the system was finished, no more floods occurred and people were able to live peacefully. Today, Dujiangyan 8. (admire) by scientists from around the world because of one feature. 9. (like) modern dams where the water is blocked with a huge wall, Dujiangyan still lets water flow through the Minjiang River naturally, making it possible for ecosystem and fish populations 10. (exist) in harmony.