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问题 选择题

把两只“220V 25W”的电灯并联在220V的电源上时总功率为P1，把它们串联在220V的电源上时总功率为P2，则（　　）

A．P1＞P2

B．P1＜P2

C．P1=P2

D．都有可能

答案

∵两电阻并联时总电阻小于任何一个分电阻，两电阻串联时总电阻大于任何一个分电阻，

∴两电阻串联时电路中的总电阻大于两电阻并联时的总电阻，

∵P=

U2
R
，且它们串联时和并联时总电阻两端的电压相等，

∴串联时的总功率小于并联时的总功率，即P1＞P2．

故选A．

阅读理解
阅读理解。
                                                  Holidays
                                                 Holiday News
     Vacancies (空位) now and in the school holidays at a country hotel in
Devon. This comfortable, friendly home-from-home lies near the beautiful
quiet countryside, but just a drive away from the sea. The food is simple but good. Children and pets are welcome. Reduced prices for low season.

                                       The Snowdonia Center
     The Snowdonia Center for young mountain climbers has a mountain
lesson. The beginners' costs are ￡57 for a week, including food and rooms. Equipment is included except walking shoes, which can be hired at a low
cost.
     You must be in good health and prepared to go through a period of
body exercises. This could be the beginning of a lifetime of lifetime of mountain
climbing adventure.

                             The World Sea Trip of a Lifetime
     Our World Sea Trip of 2008 will be unlike any holiday you have ever
been on before. Instead of one hotel after another, with all its packing and
unpacking waiting and traveling, you just go to bed in one country and
wake up in another.
     On board the ship, you will be well taken care of. Every meal will be
first-class and every cabin like your home.
     During the trip, you can rest on deck(甲板), enjoy yourself in the
games rooms and in the evening dance to our musical team and watch our
wonderful play.
     You will visit all the places most people only dream about - from
Acapulco and Hawaii to Tokyo and Hong Kong.
     For a few thousand pounds, all you've ever hoped for can be yours.
1. What can you do if you like to go on holidays with pets?
A. Choose the holiday in Devon.
B. Go to the Snowdonia Centre.
C Join the World Sea Trip of 2008.
D. Visit Acapulco and Hawaii.
2. In what way is the Snowdonia Centre different from the other two holidays?
A. It provides chances of family gatherings.
B. It provides customers with good food.
C. It offers a sport lesson.
D. It offers comfortable room.
3. What is special about the World Sea Trip of 2008?
A. You can have free meals on deck every day.
B. You can sleep on a ship and tour many places.
C. You will have chances to watch and act in a play.
D. You have to do your own packing and unpacking.
4. At the Snowdonia Centre, the beginners' costs of ￡57 do not cover  _____.
A. food
B. rooms
C. body exercises
D. walking shoes
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单项选择题

职务越高，发生的录用和安置成本会( )

A．越高
B．越低
C．无关
D．不变
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