“Eat local.” It’s one way to reduce human effect on the planet. Eating local means to try to buy and consume foods that are grown in places close to home. However, most of the food sold at supermarkets is not locally grown or produced. Trucks and planes deliver these foods from hundreds or thousands of miles away. During the transportation, greenhouse(温室)gases are produced, causing global warming. So the shorter the distance your foods must travel, the less the harm is done to the environment.
But how do you get local food if you live in a large city, hundreds of miles away from farms？Environmental health scientist Dickson Despommier and his students came up with the idea of a “vertical(垂直的)farm”.

A vertical farm is a glass-walled structure that could be built as tall as a skyscraper(摩天大楼). Since the garden is built upwards, rather than outwards, it requires much less space than an ordinary farm. The world is quickly running out of room for ordinary farming. Vertical farms could be a key to this situation. Despommier imagines a 30-story building with a greenhouse on every floor. The walls of the building would be clear, to allow crops to get as much sunlight as possible. Depending on a city’s water resources, Despommier thinks hydroponic(水培的) farming is another method for the vertical farm which needs no soil to grow plants.
Despommier says the hydroponic greenhouses would use a system that would use a city’s waste water and fill it with nutritions to make the crops grow. If this method works, it would provide food to a city and save millions of tons of water.
The idea of a vertical farm has attracted the attention of government officials around the world. Scott Stringer, a government official from New York City, thinks the city is suitable for the vertical farming. “Obviously we don’t have much land left for us,” Stringer said. “But the sky is the limit in Manhattan. ”
Despommier admits that there is still a lot of work to do to make vertical farms a reality. “But I think vertical farming is an idea that can work in a big way,” he says.
Why are people advised to eat local?

A．Because it means convenience(方便) to people.

B．Because it can help people save a lot of money.

C．Because local food has more nutrition.

D．Because it is environmentally friendly.

Which is one of the vertical farm’s benefits when compared with ordinary farming?

A．It produces healthier food.

B．It does less harm to the cities.

C．It needs less space of the city.

D．It requires less transport costs.

By saying “the sky is the limit in Manhattan”, Stringer means _____.

A．people can make full use of vertical space of Manhattan

B．there is a limit for using empty land in Manhattan

C．the height of buildings in Manhattan is limited

D．Manhattan can spread as far as possible

What can we learn about the vertical farming in the passage?

A．No soil is needed to grow plants in a vertical farm.

B．It has solved the problem of the food shortage in a big way.

C．It is a 30-story building with a greenhouse on every floor.

D．Crops are mainly grown in the rainwater in a vertical farm.