题目

二胡是中国的民族乐器，有粗(内弦)、细(外弦)两根弦，拉弓时弓毛和弦摩擦发出声音，如图所示，下列做法不能改变二胡音调的是(    ) A．用手指按压同一根弦的不同位置 B．手指按压在弦的相同位置，从摩擦内弦换到摩擦外弦 C．加大摩擦弦的力量 D．旋转弦轴，增加弦的紧张度 答案：C 【解析】 【分析】 【详解】 A．用手指按压同一根弦的不同位置，弦振动部分的长度不同，振动的频率不同，发声的音调不同，故A不合题意； B．手指按压在弦的相同位置，从摩擦内弦换到摩擦外弦，由于两根弦的粗细不同，振动的频率不同，发声的音调不同，故B不合题意； C．加大摩擦弦的力量，2．Bottled water has become the choice for people who are healthy and thirsty．Bottled water is all over the world．But some say the planet's health，and people's health may be suffering from it．The idea that bottled water is safer for humans may not be true．The Natural Resources Defense Council of America said，"There is no promise that because water comes out of a bottle，it is cleaner or safer than water from the tap．"Another New York City-based action group added that some bottled water is"really just tap water in a bottle-sometimes more clean，sometimes not．"It is not proven that bottled water is better than tap water．Nick Reeves from the Chartered Institution of Water and Environmental Management said，"The high mineral content （含量） of some bottled water makes them not good for feeding babies and young children．"Also，most bottled water doesn't have fluoride （氟化物），which can make teeth stronger．Kids are drinking more bottled water and less fluoridated tap water，and some say that's behind the recent rise in bad teeth．Storing is another problem．Placed near heat，the plastic bottles can produce bad chemicals （化学物质） into the water．According to the Environmental Protection Agency，some 2.7 million tons of plastic are used worldwide to bottle water each year．The plastic can take between 400 and 1，000 years to break down．In terms of energy use，plastic bottles are also not cheap．One report said that if water and soft drink bottlers had used 10 percent recycled materials in their plastic bottles，they would have saved about 72 million gallons of gas．So，if you are worried about the effect of bottled water on the Earth，you can take the following steps．●Drink from your tap．Unless your government warns against this，it should be fine．●Get a container （容器）．Carry your tap water in a steel or a lined drinking container，and clean it between uses．●Keep it cool．Don't drink from a bottle that has been sitting in the sun，don't store it near chemicals，and don't reuse plastic bottles．●Choose glass containers over plastic if possible．When finished，recycle!48．What is the main idea of the article？DA．Drinking tap water is the only choice for people．B．Glass containers are better than plastic bottles．C．Plastic bottles are harmful to the environment．D．Bottled water may not be as good as we think．49．What can we learn about plastic bottles from the article？CA．They break down in less than 300 years．B．They can be used for many other things．C．They are a risk to the environment．D．They are cheap to make．50．According to the article，we can know that bottled water isBA．no problem for the environment        B．more expensive than tap waterC．always safer than tap water            D．better for babies51．Which of the following about tap water is NOT mentioned in the article？AA．There are a lot of problems storing tap water．B．Bottled water can be just tap water in a bottle．C．It may be better for your teeth．D．It may contain fluoride．