将肥皂膜放在正在放音的音箱前边，可看到肥皂膜在_________，说

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问题填空题

将肥皂膜放在正在放音的音箱前边，可看到肥皂膜在_________，说明声音是一种波动，并且_________能量。有一种超声波牙刷，能发射一种超声波，这种超声波可以穿过牙齿周围的液体引起强烈的振动，从而将牙齿上的污垢清除下来而不会损坏牙齿，使用超声波是因为它产生的振动比可闻声_________。

答案

振动；能传递；更强烈

问答题

Most marketing operations pay close attention to what young people are buying and thinking. Not Britain’s political parties, however, for the simple reason that the under-30s are unlikely to go anywhere near a polling booth. In 1964, 11% of those aged 18 to 24 claimed not to vote, according to the British Election Study. At the general election last year that figure rose to 55%. 46. A report this week by Reform, a think-tank, suggests that this reticence is costing them dearly. Changes in government policy, it argues, have turned being young into a terrible bore.

47. There are already two powerful economic forces working against the so-called "IPOD generation" that are beyond the government’s control. First, the ageing of the population is fast increasing the ratio of people in retirement to those of working age. So the young can look forward to handing over a rising proportion of their pay to support the oldies in their decline. Second, the cost of buying a house in places where people want to live has shot up beyond the reach of the young. In 1995 24% of all first-time homebuyers were under 25 ; today, less than 15% are, according to the Halifax, a bank.

This much is uncontroversial. But the report also argues that the Labour government has made life worse for young people, in three ways. First, increased spending on health care has tended to benefit the old, who ’use the NHS more than the young. Second, tilting the tax and benefit system towards people with children has transferred money from the young to the middle-aged. Third, higher tuition fees are landing university graduates with hefty debts. 48．And the future doesn’t look much better: the government’s proposed pension reforms, along with the decline of defined-benefit company-pension schemes, make grim reading for the under-30s too.

"These changes ought to have brought about a re-examination of the burden of taxation on this age group," says Nick Bosanquet of Imperial College London, one of the authors of the report, tie reckons that, after paying various taxmen and lenders, graduates take home only around half of their salaries. The average for all salaried workers is about three-fifths.

Are things really that bad When examined in a freeze-frame, being young does not look much fun financially. But welfare states are meant to transfer resources from the vigorous to the fragile. Some benefits are merely deferred: today’s 25-year-olds will have babies and hip replacements one day. 49．And although people in their 20s and 30s tend to be heavily indebted this passes when they sink into their 40s and 50s, says Richard Disney of Nottingham University.

Even so, the feeling that young people are being squeezed presents a political opportunity for the opposition parties. 50．David Willetts, the Conservative shadow education secretary, said in a speech last year that the young "could be forgiven for believing that the way in which economic and social policy is now conducted is little less than a conspiracy by the middle- aged" against them_. The Liberal Democrat commission on tax policy worried in August about inter-generational unfairness too.

There will be more of such talk. For the Tories, it offers a way to discuss reducing spending without sounding as if they are merely the mouthpiece of the wealthy. It gives Lib Dem leaders a way to argue activists out of promising to out-spend Labour. And it might even persuade some of those gloomy 25-year-olds to vote.