题干

如图甲所示是水位监测装置的原理图.柱形绝缘容器A内部左右两面插有竖直薄金属板并与电路连接,底部有一小孔与湖水相通,且容器底面与警戒水位相平.已知电源电压恒为6 V,小灯泡标有“2 V  2 W”字样(不考虑温度对灯丝电阻的影响).两金属板间的湖水电阻R与x的关系如图乙所示(x为容器内水柱高度h的倒数,即x=1/h).则下列说法中正确的是 (   )

A:容器内水柱越高,电表的读数越小

B:将电流表改为水位计,水位计的刻度是均匀的

C:当湖水水位高于警戒水位5m时,灯泡正常工作

D:当湖水水位高于警戒水位0.4m时,电流表示数为0.6A

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C

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    Leaving Hanoi on a fiercely hot summer day,after an hour by air,Luang Prabang gradually appears below our airplane wings.From a few hundred meters above,my first impression of this UNESCO-listed heritage(遗产)is an area of green land and mountains,surrounded by snaking rivers.

    Encircled by mountains,the former royal capital of Luang Prabang is more than just the country's picture-perfect showpiece.

    Travelers will be attracted to Luang Prabang by the city's timeless peacefulness with its shiny Buddhist temples, French colonial architecture and friendly people.

    Tourists visiting Luang Prabang shouldn't miss the chance to see one of the most sacred(神圣的)Lao traditions, tak bat,or the Buddhist almsgiving ritual(仪式),which dates back to the 14th century.

    As the sun rises in Luang Prabang,hundreds of Buddhist monks depart from their temples to gather their daily offerings,which most commonly are rice,fresh fruit and traditional sweet snacks.The daily alms gathering begins on the main street before spreading to all the side streets.

    Our group of six got out of our comfy beds at 5 am to join other local residents and tourists to offer alms to the monks.We kneeled by the roadside in front of the 3 Nagas Hotel on the main street with big baskets of steamed sticky rice,waiting quietly until monks of all ages passed by to accept our gifts.

    The daily ritual gives you a wonderful opportunity to experience an ancient Lao tradition.However,there are some strict rules if you wish to join the event.

    Firstly,shoulders,chests and legs must be covered in modest clothing as a mark of respect.You should also remain a suitable distance from the monks.Photographs may be taken,but from a distance and never use a camera flash.The ritual has to be performed in silence.Talking to or touching the monks at any time,even when making an offering,is not allowed.

    Another must-do morning activity is to visit the local market,where you can see the generosity that Mother Nature offers this dreamy land.While walking through the morning market,located within a long and narrow hamlet,I was excited to see all kinds of products from the nearby river and jungle: some ill-fated squirrels lying next to fresh bamboo shoots,different kinds of wild mushrooms and vegetables displayed on banana leaves and giant river catfish in baskets.

    Although Luang Prabang is small,there are many things to see here.Active travelers can get up close and personal with Laos' gentle giants at the elephant conservation camp or take in some scenes of riverside life with a cruise or kayak excursion on the rivers.Two waterfalls that are perfect for picnicking in the foothills nearby,and classes are available in traditional crafts.