The challenge set by Bill Gates was to come up with a latrine which works without running water, electricity or aseptic tank. It also needed to operate for less than 5 cents. 28 designs were displayed at the recent Reinvent the Toilet Fair, in Seattle, USA. Among them was one which turned human waste into electricity using microwaves, another which converted human waste into charcoal, and yet another which used urine for flushing.

　　But the winner was a solar－powered design which generated hydrogen gas and electricity. The team from the California Institute of Technology (CIT) picked up a prize of ，000.ut clearly Bill Gates doesn't feel he's flushing money down the toilet. After the Seattle event he said, “We couldn't be happier with the response we've gotten.” Gates has even pledged $370 million (2.2 billion RMB) more to the future toilet project. They hope to field test more prototypes over the next three years.

　　21．Why is Bill Gates paying people to invent new toilets?

　　A．Because he wants to test people's sense of creativity.

　　B．Because he wants to improve sanitation for many people.

　　C．Because he thinks the traditional ones are out of fashion.

　　D．Because he can't design this kind of things himself.

　　22．Which of the following is NOT a problem with the traditional flush toilets?

　　A．They waste too much water.

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