20.Seeing the driver break the traffic rules,the policeman ______ to the driver to stop.

A.spoke¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ B.signed

C.made¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ D.let

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A lot of water is needed in large cities.Some cities get water from ¡¡21¡¡ .Some get water from lakes or rivers ¡¡22¡¡ .But some cities have to get water from lakes or rivers far away.

Water is usually ¡¡23¡¡ to a city from a place higher than the city¡¡ ¡¡24¡¡ .When water is found only in a ¡¡25¡¡ place,it must be pumped up to the city.Then it is sent to each home.

¡¡ 26¡¡ are often built in a river to keep the water from flowing away.Then a new lake is ¡¡27¡¡ .People know how much water they need,and allow ¡¡28¡¡ water to flow away below the dam.In this way the city stores water for its use.

There is usually a building near the dam,¡¡ 29¡¡ much important work is done.For example,the water is tested ¡¡30¡¡ it is piped to the city.

We must¡¡ ¡¡31¡¡ the water clean before we drink it.Sometimes¡¡ ¡¡32¡¡ must be taken away from it.Sometimes medicine must be added to it.Machines mix these ¡¡33¡¡ things with the water.In this way,it is made drinkable.

In¡¡ 34¡¡ hotels,you usually find three taps.One is for cold water,¡¡ 35¡¡ is for hot water and the third is for iced water.

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