3D technology has now hit its third era of mainstream popularity. But unlike the 3D technology in th

3D technology has now hit its third era of mainstream popularity. But unlike the 3D technology in the 1950s or the 1980s, the current 3D market doesn't seem to be about to crash.
The next market for 3D movies appears to be the home market. While some home video releases have included anaglyph （立体）glasses, consumers have only recently had the chance to buy true 3D-capable televisions. 3D-ready televisions offer a 3D mode that works with a pair of battery-powered LCD shutter lenses. These glasses differ from polarized lenses（偏光镜片）as they contain liquid crystal displays that are synchronized（同步）with the video display to let light pass through at specific intervals. Shutter lenses have to be kept synchronized with the display either through a cable or wireless signal.
Despite recent advances in technology, 3D remains an imperfect and relatively expensive technology. People who like watching TV often blame the fact that 3D versions of films aren't as sharp or rich in color as their 2D versions. Polarized glasses also reduce peripheral vision（周边视觉）and leave viewers focused on the center of the screen. Newer 3D technologies will hopefully overcome these shortcomings.
Besides modest improvements, 3D producers are also working to break through the next significant barrier in 3D display. A number of auto stereoscopic （自 动立体的） displays are currently being designed. Like stereoscopic screens, auto stereoscopic screens display two images that are merged into one to cause a 3D effect. However, auto stereoscopic screens get rid of the need for glasses entirely. Using lenticular （透镜的） screens, auto stereoscopic displays produce a changeable image depending on the angle at which a person views the screen.
To date, this technology is only being employed for smaller devices like cellphones. Currently, the auto stereoscopic effect is difficult to achieve on larger screens because it requires the viewer to view the screen from a direct and constant angle. But at the current rate of advancing technology it shouldn't be too long before viewers are able to sit down at home or in a theater and enjoy a true 3D experience without the need for glasses.
12．What do we know about the liquid crystal displays?
A．They let the light from the screens through at any time.
B．They function when the video display is working.
C．They are built into the polarized lenses.
D．They can reduce peripheral vision on the screen.
13．What shortcoming do recent 3D versions of films have?
A．They are not available in the market now.
B．They are watched through polarized glasses.
C．Their images aren't clear and colorful.
D．Viewers have to centre on the screen.
14．Unlike stereoscopic screens, what features do auto stereoscopic screens have?
A．They make viewers focus on the screen centre.
B．They display two images merged into one.