理想变压器原线圈接在如图所示的电压上,原副线圈匝数之比为10:1,串在原线圈上的

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问题:

理想变压器原线圈接在如图所示的电压上,原副线圈匝数之比为10:1,串在原线圈上的电流表的示数为1A,则以下叙述正确的是(  )

A.变压器输出功率为200W

B.若n1=100匝,则输出端线圈的磁通量变化率的最大值为2Wb/s

C.副线圈两端的电压表示数20V

D.变压器的输入功率是由发电厂的输出功率决定的

考点:变压器的结构和原理
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房屋征收主体是()。

A.国务院

B.建设部

C.各地区的拆迁办

D.各地的市、县级人民政府

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2011年7月,省委书记孙春兰回信给()。

A.古田县实验小学少先队员

B.上杭县实验小学少先队员

C.寿宁县实验小学少先队员

D.永定县实验小学少先队员

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The view over a valley of a tiny village with thatched (草盖的) roof cottages around a church, a drive through a narrow village street lined with thatched cottages painted pink or white, the sight over the rolling hills of a pretty collection of thatched farm buildings―these are still common sights in parts of England. Most people will agree that the thatched roof is an essential part of the attraction of the English countryside.

Thatching is in fact the oldest of all the building crafts(工艺)practised in the British Isles. Although thatch has always been used for cottage and farm buildings, it was once used for castles and churches, too.  

Thatching is a solitary(独自的)craft, which often runs in families. The craft of thatching as it is practised toady has changed very little since the Middle Ages. Over 800 full-time thatchers are employed in England and Wales today, keeping and renewing the old roofs as well as thatching newer houses. Many property owners choose thatch not only for its beauty but because they know it will keep them cool in summer and warm in winter.

In fact, if we look at developing countries, over half the world lives under thatch, but they all do it in different ways. People in developing countries are often unwilling to go back to traditional materials and would prefer modern buildings. However, they may lack the money to allow them to get the necessary materials. Their temporary mud huts with thatched roofs of wild grasses often only last six months. Thatch which has been done the British way lasts from twenty to sixty years, and is an effective defiance against the heat.

小题1:Which of the following remains a special feature of the English countryside?

A.Narrow streets lined with pink or white houses.

B.Rolling hills with pretty farm buildings.

C.Cottages with thatched roofs.

D.Churches with cottages around them.小题2:What do we know about thatching as a craft?

A.It is a collective activity.

B.It is practised on farms all over England.

C.It is quite different from what it used to be.

D.It is in most cases handed down among family members.小题3:Thatched houses are still preferred because of _________.

A.their style and comfort

B.their durability

C.their easy maintenance

D.their cheap and ready-made materials小题4:People in developing countries also live under thatch because ________.

A.thatched cottages are a big tourist attraction

B.thatched roof houses are the cheapest

C.thatch is an effective defense against the heat

D.they like thatched houses better than other buildings

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离心泵停泵时,先关出口阀是为了()。

A、防止出口液体倒流

B、防止泵倒转

C、使停泵电流最小

D、因为没有止回阀

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简述造成信号波动的可能原因

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