And homes can be responsible for up to 25 percent of a nation’s total energy use. But there are surprisingly simple ways to greatly reduce energy use, its cost, and its effect on the environment.A solution to this problem is called passive home (or passive house). An expert says the design of a passive house aims to reduce energy demand to its lowest possible level. Passive houses use no solar, geothermal (地热) or wind energy equipment, but they are really energy-efficient.Building a passive house needs some particular products. They also need to have special air treatment systems. Supporters say they cost about 5-8 percent more than traditional homes, but they use only 10 percent of the energy for heating and cooling. Even greater savings can be reached with additions like solar water heating systems.With continuous efforts and progress, an advanced passive home that can cut heating and cooling costs by about 90 percent now can look just like any other home despite using specialized materials. The expert says, “That is the beauty of the passive house approach. You don’t have to build in a particular way or style.”It is said that you can find passive homes all over the world. The first passive design was an apartment building in Darmstadt, Germany. Two physicists helped develop it about 30 years ago. A passive house was built in Arlington, Virginia, seals its windows against leaks so that they are airtight and each window has three layers of glass. On a cold winter day, the temperature inside the unfinished home is a comfortable 12 degrees. While in the area with high temperatures, North Africa, for example, there is a passive house community designed for very hot, dry climates. And that’s a whole other area of exploration for passive houses.1.According to the passage, what is the most important feature of passive houses?

Heating and cooling equipment is the biggest user of energy in our homes. And homes can be responsible for up to 25 percent of a nation’s total energy use. But there are surprisingly simple ways to greatly reduce energy use, its cost, and its effect on the environment.

A solution to this problem is called passive home (or passive house). An expert says the design of a passive house aims to reduce energy demand to its lowest possible level. Passive houses use no solar, geothermal (地热) or wind energy equipment, but they are really energy-efficient.

Building a passive house needs some particular products. They also need to have special air treatment systems. Supporters say they cost about 5-8 percent more than traditional homes, but they use only 10 percent of the energy for heating and cooling. Even greater savings can be reached with additions like solar water heating systems.

With continuous efforts and progress, an advanced passive home that can cut heating and cooling costs by about 90 percent now can look just like any other home despite using specialized materials. The expert says, “That is the beauty of the passive house approach. You don’t have to build in a particular way or style.”

It is said that you can find passive homes all over the world. The first passive design was an apartment building in Darmstadt, Germany. Two physicists helped develop it about 30 years ago. A passive house was built in Arlington, Virginia, seals its windows against leaks so that they are airtight and each window has three layers of glass. On a cold winter day, the temperature inside the unfinished home is a comfortable 12 degrees. While in the area with high temperatures, North Africa, for example, there is a passive house community designed for very hot, dry climates. And that’s a whole other area of exploration for passive houses.

1.According to the passage, what is the most important feature of passive houses?
A. They use solar, geothermal and wind energy.
B. They are built with advanced materials.
C. They reduce energy use to a great extent.