用方框内单词的适当形式填空。

1．London is a most beautiful city in Britain, ________ on the River Thames．

2．Town twinning ________ are perhaps most useful for students and people who want to practice speaking another language．

3．In terms of size and population, how big is the ________ Union compared with China?

4．Although ________ countries give some financial help, they need to give much more．

5．________, the countries that give the most money are the Netherlands, Norway and Sweden．

6．When the lava reached the sea, there was the ________ of a huge tidal wave which could flood half the island．

7．On average, there are 800 tornadoes in the US each year, causing about 80 deaths and 1,500 ________．

8．The most serious of the earthquakes ________ in Hua County in Shaanxi Province in 1556．

9．Sandstorms in China appear to have increased in recent years as a result of“________”．

10．The Three Gorges Dam is the largest hydro-electric dam in the world, more than 1.5 kilometers wide across the Yangtze River, the world's ________ longest river．