Dickson Despommier, a public health professor at Columbia University in New York City developed an idea with his students nine years ago. They imagined people in cities growing crops inside a tall building. Tomatoes could grow on one floor of the skyscraper(摩天大楼), potatoes on the next, small animals and fish on the floor above.
This vertical(垂直的) farm, or "farmscraper", could have space for restaurants and other places that serve food, like schools or hospitals. They could serve foods that are truly locally grown.
But why would anyone want to build a farm indoors in a city? Dickson Despommier believes it will become necessary. The world needs to find places to produce enough food to feed the growing population. Space, he says, is an all-important issue.
The professor also points to the problems of traditional farms. They use a lot of freshwater. Their fertilizer and animal waste can pollute water resources. And their growing seasons can be limited.
But inside the vertical farm, crops could grow all year. And there would be no wind to blow away soil. Farmers would not have to worry about too much or too little rain, or about hot summers, freezing winters or insects. And without insects there would be no need for chemicals to kill them.
Farm machines that .use fossil fuels, like tractors, would not be needed either. And water could be recycled for drinking. "The vertical farm reuses everything, so there is no waste," says Professor Despommier.
Even buildings could be saved. Old buildings could become new farms and provide jobs.
The professor has been actively proposing the idea to cities as far away as Dubai and Canada. But so far it exists only in plans and drawings, and a model at the Museum of Science and Industry in Chicago.
Critics say building a farmscraper would cost too much, especially considering the price of land in many cities. Dickson Despommier estimates the cost at about twenty to thirty million dollars.
But he says the building would not have to be very tall. And his graduate students have found many empty lots and unused buildings in New York City that could provide space.
According to the passage the purpose of proposing the idea of a farm scraper is to      .

A．find places to produce enough food

B．serve food that are truly locally grown

C．prevent polluting the limited land

D．save fresh water

Which is one of the advantages of a farm scraper?

A．It costs less

B．It saves labor power.

C．It consumes too much energy

D．It is more environmentally friendly.

Those against the idea of farm scrapers argue that

A．it uses too much land in cities

B．it costs too much to build one

C．it causes people to lose their jobs

D．it exists only in unrealistic plans

Which of the following is true according to the passage?

A．A vertical farm has been built in Chicago.

B．Old buildings could be changed into new farms.

C．Traditional farms use less water but pollute more water

D．There are some vertical farms being put into use in Canada.