－What are those?

－They are battery-operated slippers. They ________ in the dark.

[　　]

Julia: Hi, Clinton.

Clinton: Hi, Julia.

Julia: Do you know shoes 1　　    adjustable heels?

Clinton: Yes.

Julia: 2 　　　　3　　    they invented4　　    ?

Clinton: Jayce Coziar and Jamie Ellsworth.

Julia: Then what is it used 5　　    ,do you know?

Clinton: 6　　    the style of a shoe.

Julia: Oh, I see. What about battery-operated sneakers, 7　　    and 8　　    ?

Clinton: Julie Thompson, it’s used for 9　　    in the dark.

Julia: Oh, then how about heated ice cream scoop?

Clinton: Chelsea Lemmon, and 10　　    really cold ice cream.

Battery-operated slippers are used ______ seeing in the dark.

Battery-operated slippers are used ______ seeing in the dark.

A．to               B．as               C．by               D．for

Electric bicycles which run on battery-operated (电瓶) motors are winning over riders of ordinary bikes   41 their speed, quality and environmental advantage.
They were first   42 on 1980s in China, but the selling was not very good. Today, thanks 43  improvements on battery quality, the electric bikes sell well. There are now more than 100 electric bicycle producers in China and 26 million such bicycles were produced in 2011. Japan is another large  44  of such bicycles in the world with a total production reaching 381,721in 2010.
  45 China is one of the largest producers of electric bicycles in the world, the   46  of its producers with mass production (大批量生产) is actually small.
Electric bicycles are still   47 in China. Time is needed for people to become familiar with them and accept them. Each bike’s price of between 2,000 yuan (US $318) and 3,000 yuan (US $477) is still  48  for ordinary citizens (民众). Although such bikes are quick, safe and 49 to operate, their batteries still have shortcomings (不足). They weigh more than 10 kilograms; their service life is   50  two years and they   51  400 yuan each.
There were more than 450 million bikes in China in 2006. If just one percent of all these bikes are replaced by electric  52  , the market will be very large. And   53  the battery is further improved and the price is    54   , many of us will not be able to keep back from    55  the latest electric bikes