练习：
1. Which of the following statements does not indicate the importance of windows as described in the first two paragraphs?
A) Windows can change from clear to dark to save energy.
B) Windows help to save energy by letting light in.
C) Windows help to save energy by providing heat.
D) Windows enable people to have contact with the outside world.
2. When are windows the weak link in a building?
A) In the cold winter.
B) In the hot summer.
C) When air conditioners are turned on.
D) Both A and B.
3. What are smart windows， according to Paragraph 4?
A) Windows that are coated.
B) Windows that are glazed.
C) Windows the color of which can be changed.
D) Windows that have many layers.
4. To make electrochromic windows change color， what is applied to the window glass?
A) Electricity.
B) Tungsten oxide.
C) A battery.
D) A voltage.
5. What will be the benefit if the research on smart windows turns out to be successful， according to the last paragraph?
A) The buildings will look different.
B) Windows can be as large as you want.
C) We may not need air conditioners any more.
D) They are less expensive than traditional windows.