题目

如图所示为t=0时刻简谐横波a与b的波形图，其中a沿x轴正方向传播，b沿x轴负方向传播，波速都是10m/s，振动方向都平行于y轴．下图画出的是平衡位置在x=2m处的质点从t=0开始在一个周期内震动的图象，其中正确的是（ ）A．B．C．D． 答案：BThe following is a recent survey among teenagers:RadioMost teenagers nowadays are not regular listeners to radio. They may occasionally tune in, but they do not try to listen to a program specifically. The main reason teenagers listen to the radio is for music, but now with online sites streaming music for free they do not bother, and users can choose the songs they want instead of listening to what the radio presenter/DJ chooses. TelevisionMost teenagers watch television, but usually there are points in the year where they watch more than average. This is due to programs coming on in seasons, so they will watch a particular show at a certain time (as long as it lasts) but then they may watch no television for weeks. Teenagers are also watching less television because of services such as BBC iPlayer, which allows them to watch shows when they want. Whilst watching TV, adverts come on quite regularly (18 minutes of every hour) and teenagers do not want to watch these, so they switch to another channel, or do something else whilst the adverts run. NewspapersNo teenager that I know of regularly reads a newspaper, as most do not have the time and cannot be bothered to read pages and pages of text while they could watch the news summarized on the Internet or on TV. InternetEvery teenager has some access to the Internet, be it at school or home. Home use is mainly used for fun (such as social networking) whilst school (or library) use is for work. Most teenagers are heavily active on a combination of social networking sites. Facebook is the most common, with nearly everyone with an Internet connection registered and visiting >4 times a week. Facebook is popular as one can interact with friends on a wide scale. For searching the web, Google is the dominant figure, simply because it is well known and easy to use. Some teenagers make purchases on the Internet (on sites like eBay) but this is only used by a small percentage, as a credit card is required and most teenagers do not have credit cards. Many teenagers use YouTube to watch videos (usually anime which cannot be watched anywhere else) and some use it as a music player by having a video with the music they want to listen to playing in the background. Mobile Phones99pc of teenagers have a mobile phone and most are quite capable phones. Usually, teenagers only use their phones for texting, calling. Features such as video messaging or video calling are not used—because they are expensive.Services such as instant messaging are used, but not by everyone. It usually depends whether the phone is Wi-Fi compatible, because otherwise it is very expensive to get Internet off the phone network. As most teenagers’ phones have Bluetooth support, and Bluetooth is free, they utilize this feature often. Mobile email is not used as teenagers have no need; they do not need to be connected to their inbox all the time as they don’t receive important emails. 【小题1】   The survey carried out recently is mainly concerned with ______.A．how teenagers consume mediaB．what electric devices teenagers favorC．which new trend teenagers are followingD．how teenagers contact others and make their social net【小题2】   As is mentioned in the survey, the reason why teenagers watch less TV mainly lies in that ______.A．teenagers do not watch regular programsB．all the TV programs are on for only a few weeksC．teenagers may turn to other devices to watch their favoriteD．the TV adverts coming on every channel are just the same【小题3】   Which of the following is TRUE according to the survey?A．Radio presenter or DJ used to invite the listeners to choose the songs they want.B．The main source for teenagers to get news is Internet as well as newspapers.C．Google is the most common social networking sites due to its convenience.D．Some features of modern mobile phones are not widely used by teenagers.