题目内容：
请阅读下面材料,完成第小题。An Earthship is a home that is built of materials such as old tire and aluminum cans.It is the i-dea of a man n锄ed Michael Reynolds．Many Earthships are more or less self-sufficient because they Drovide their own heat，air and water．They oflen have gardens watered and fed by wastewater.They are comfoaable and ecologically friendly．
The main material used in building Earthships is tires．Tires are plentiful and call’t be recycled tike paper，plastic，and metal．While building supplies for most houses call be very expensive，old used tires are free．First，the tires are packed tightly with dirt．Each full tire weighs as much as 400 Dounds．The tires are then stacked like bricks．The waHs are extremely strong．They also help keep an even temDeratul．e in the house(between 60 and 70 degrees)without heating and cooling systems.
The walls inside the Earthship are made of aluminum cans that are held together by cement.Then they are coated with adobe or stucco．
The mofs of Earthships are sloped so that rain and snow run into large tanks．These tanks hold all the water for the house，and pumps push the water through the pipes．Sometimes，water flows in certain areas of the house as waterfalls!Water that has been used is pumped out into the gardens where owners grow much of their own food．
In most of these houses，the southern side has huge windows that take in winter sunlight as a source of heat．Summer sun does not come in through the south windows，so it doesn’t get too hot in the summer．The house also has solar panels that gather energy for lights and hot water and cooking．
The Earthships have all the comforts of a regular house without the high cost of electric bills!
In a time when we are running out of energy resources，pollution is bad，and waste is piling up，Earthships are t ile best places to live in．For people who truly care about the environment，Earthships provide a great alternative to traditional houses．You won’t be giving up any comforts，and the styles are attractive．We all hope that more and more people will build Earthships and take a huge step to-
ward helping the environment and saving our planet．
What is the main idea of this passage? A．Earthships are a good way to live and protect the environment．
B．Tanks hold water collected from rain and snow．
C．It's important to grow your own food in a vegetable garden．
D．People who live in Earthships usually live in the desert．
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