题目内容：

Physics could soon make it possible to replace those heavy glass lenses（镜头）on cameras with “metalenses” －materials engineered to focus light at a fraction（少量）of the weight and size of traditional lensing.

A team from Harvard University’s school of engineering has designed a metalens that can focus nearly the entire visible light. Previous metalenses could focus only narrow color wavelengths, or wavelengths outside the visible.

When light moves through glass, the different wavelengths that make up the light slow at different rates. This causes their paths through the glass to bend, so that they separate. Pass a beam of white light through a prism（棱镜）, and this effect will cause a rainbow to burst out the other end. This presents a challenge to lens makers; a single focusing element will project a picture that has colors from red to violet hitting different spots on the film.

So, modem camera lenses use many different glass elements to reverse that effect, pushing the different wavelengths of light back onto a single focal point, although that doesn’t work perfectly; many photographers know the pain of buying an expensive lens only to find a violet edge around the subjects in their photographs.

A metalens takes a different approach to focusing light. Instead of using the reflection of glass, a metalens uses tiny structures, typically made of titanium dioxide（二氧化钛）, to bend wavelengths toward the metalens focal point. In the past, though, metalenses could bend just one wavelength at a time, or in more advanced cases, a narrow band of the visual light. The newly created metalens bends nearly the full.

Metalenses have other challenges to overcome before they can compete seriously with traditional glass. The most significant one: resolution（分辨率）, according to a journal article. None of the metalenses so far are particularly sharp compared with their best glass competitors. But, again, as the technology progresses, it could address that limitation. Metalenses might not land on store shelves anytime soon, but they are coming.

1.What do we know about the “metalenses” from Paragraph 1?

A. It’s small.    B. It’s expensive.

C. It’s visible.    D. It’s narrow.

2.Why is it tough in making lens?

A. Light is low at different rates.

B. Light path is bent when light travels.

C. An image has colors from red to violet.

D. White light will cause different colors.

3.What does the underlined word “reverse” in Paragraph 4 mean?

A. Change.    B. Exchange.

C. Increase.    D. Improve.

4.What’s unique in ways of focusing light for a new metalens?

A. It throws the glass light back.

B. It uses metals in the structure.

C. It nearly makes the visual light all bend.

D. It is more advanced and narrow.