crop planning uncertain.Farmers in many parts of the world already are using water available to the last drop.And the world is getting more crowded：by mid­century，the global population will grow from 6.8 billion to 9 billion.

　　To feed so many people may require expanding farmland at the expense of forests and wilderness，or finding ways to completely increase crop output.

　　Gertjan Meeuws has taken the concept of a greenhouse a step further，growing vegetables and house plants in enclosed (封闭的) and regulated environments.In their research station，water flows into the pans when needed，and the temperature is kept constant.Lights go on and off，creating similar day and night，but according to the rhythm of the plant.

　　A building of 100 square meters and layers (层) of plants could provide a daily diet of 200 grams of fresh fruit and vegetables to the entire population of Den Bosch，about 140,000 people.Their idea isn't to grow foods that require much space，like corn or potatoes.

　　Here sunlight is not only unnecessary but can be harmful.Plants need only specific wavelengths of light to grow.Their growth rate is three times faster than under greenhouse conditions.They use about 90 percent less water than outdoor agriculture.And city farming means producing food near the consumer，and there's no need to transport it long distances.

【语篇导读】　本文是一篇说明文。本文主要讲述了研究者Gertjan Meeuws和他的几位同事所研究的一种未来农业模式：不需要阳光和雨水的室内农业，它不同于温室农业，是一种节能、节水和环保的农业模式，具有适应性强、成本低等特色。

16．What can we mainly learn from Paragraph 2?

　　A．The climate is worse and worse.

　　B．The city people live a hard life.

　　C．The world has difficulty feeding its people.

　　D．The world's population is increasing fast.

答案　C　[细节理解题。本段主要列举了世界在满足人类食品需求方面的问题，如城市人口挨饿问题、物价上涨和不稳定问题以及人口增长所带来的问题等。选项A、B、D只是世界供应粮食这一大问题中的几个小问题，答案应选C。]

17．Which of the following is true of the environments in the research station?

　　A．The temperature is often changed.

　　B．Sunshine is in great need for plants.

　　C．Day and night depends on plants.

　　D．Air quality is controlled by plants.

答案　C　[细节理解题。文章第四段中的the temperature is kept constant表明这个温度不会经常变化，故A不对；文章最后一段中的sunlight is not only unnecessary表明这