The Green Microgym in Portland，Oregon has all the usual stuff you'd expect-sweaty people，loud music，smooth exercise equipment-but it has some extras as well. Everywhere you look，there are power wires. And these aren't the typical kind that let you surf the Web while you ride a spin cycle-although. you can do that too．The gym uses special exercise equipment that captures（捕获）the energy you create while riding, converts（转换）it into electricity and channels it into the power outlets（插座）．
The idea of using exercise equipment to produce electricity is not new. A gym in Hong Kong has been doing this since 2007. But clean (and healthy）energy is just now starting to catch on in U. S. gyms·"We have seen a significant increase in interest in the past six months，which is a good sign that fitness centers are ready to spend money on green technologies，” says Mike Curnyn，co-founder of the Green Revolution，a Connecticut-based firm that wires bikes into a central battery that can store energy.
The Green Microgym，first opened in 2008，has more than 200 members and is doing so well that owner Adam Boesel opened another one five miles from the original．Although membership costs about the same as ordinary gyms，customers can earn gift certificates from local businesses for watts produced while exercising．An average workout creates 37. 5 watt hours，which is enough to power a phone for a week．
Boesel uses spin bikes made by Resource Fitness，a Seattle company he co-owns，that captures energy produced from the flywheel. Wires send the converted AC current（交流电流）into any standard wall outlet-for this reason，the product line's name is Plug Out-and the energy created is used before the building draws power from the grid（电网）．Unlike the Green Revolution equipment，Plug Out machines cannot store extra energy. A third company，the Florida-based ReRev，is adding converters to a specific brand of spin bikes. But since the converters add＄1，000 to the price of the equipment，the ReRev and Green Revolution machines are at a disadvantage．
Resource Fitness，by contrast，sells its equipment for the same＄1，200 price as non- electricity-producing machines，removing the question of how long it will be until the energy savings pay for the cost of the unit．The company can afford to do this because its designs don’t call for the extra wiring needed for battery packs and large converters．It is also trying to price competitively with standard equipment so more gyms-and gym goers-will make the switch．
Members of the Green Microgym earn gift certificates for_______．

A．using the man-powered exercise equipment

B．saving electricity for local businesses

C．producing green electricity to power their phones

D．paying higher membership fees

The spin bikes made by Resource Fitness are different from those by Green Revolution in that_______.

A．they are easier to ride

B．they are more expensive

C．they don't have wires connected

D．they can not store extra electricity

What might prevent the green exercise equipment from getting more popular？

A．People's unwillingness to go green．

B．The high cost of making it.

C．Safety problems concerning electricity.

D．Lack of certificates．

The underlined words“make the switch”in the last paragraph most probably mean_____.

A．change to a different gym

B．use green exercise equipment

C．switch on the spin bikes

D．add a battery to the machine