15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 75)

These days, most people in Britain and the US do not wear very formal clothes. But sometimes it is important to wear the right thing.

Many British people don't think about clothes very much. They just like to be comfortable. When they go out to enjoy themselves, they can wear almost anything. At theatres, cinemas and concerts you can put on what you like from elegant suits and dresses to jeans and sweaters. Anything goes, as long as you look clean and tidy.

But in Britain, as well as in the US, men in offices usually wear suits and ties, and women wear dresses or skirts (not trousers). Doctors, lawyers and business people wear quite formal clothes. And in some hotels and restaurants men have to wear ties and women wear smart dresses.

In many years, Americans are more relaxed than British people, but they are more careful with their clothes. At home, or on holiday, most Americans wear informal or sporty clothes. But when they go out in the evening, they like to look elegant. In good hotels and restaurants, men have to wear jackets and ties, and women wear pretty clothes and smart hairstyles.

It is difficult to say exactly what people wear informal or formal in Britain and the US, because everyone is different. If you are not sure what to wear, watch what other people do and then do the same. You'll feel more relaxed if you don't look too different from everyone else.

Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a drive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper. The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth in seawater, so that at 39 meters in seawater a diver is exposed to pressure of about 4 atmospheres. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meter are present at five times their usual pressure. Nitrogen, which composes 80 percent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmospheres, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen dissolved in the blood. Deep dives are less dangerous if helium is substituted for nitrogen, because under these pressures helium does not exert a similar narcotic effect.

As a scuba diver descends, the pressure of nitrogen on the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues The reverse occurs when the diver surfaces, the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints.

Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend and even rupture. This condition is called air embolism.

To avoid this event, a diver must ascend slowly, never at a rate exceeding the rise of the exhaled air bubbles, and must exhale during ascent.

Music can bring us to tears or to our feet, drive us into battle or lull us to sleep. Music is indeed remarkable in its power over all humankind, and perhaps for that very reason, no human culture on earth has ever lived without it. From discoveries made in France and Slovenia, even Neanderthal man, as long as 53,000 years ago, had developed surprisingly sophisticated, sweet-sounding flutes carved from animal bones. It is perhaps then, no accident that music should strike such a chord with the limbic system – an ancient part of our brain, evolutionarily speaking, and one that we share with much of the animal kingdom. Some researchers even propose that music came into this world long before the human race ever did. For example, the fact that whale and human music have so much in common even though our evolutionary paths have not intersected for nearly 60 million years suggests that music may predate humans. They assert that rather than being the inventors of music, we are latecomers to the musical scene.

Humpback whale composers employ many of the same tricks that human songwriters do. In addition to using similar rhythms, humpbacks keep musical phrases to a few seconds, creating themes out of several phrases before singing the next one. Whale songs in general are no longer than symphony movements, perhaps because they have a similar attention span. Even though they can sing over a range of seven octaves, the whales typically sing in key, spreading adjacent notes no farther apart than a scale. They mix percussive and pure tones in pretty much the same ratios as human composers – and follow their ABA form, in which a theme is presented, elaborated on and then revisited in a slightly modified form. Perhaps most amazing, humpback whale songs include repeating refrains that rhyme. It has been suggested that whales might use rhymes for exactly the same reasons that we do: as devices to help them remember. Whale songs can also be rather catchy. When a few humpbacks from the Indian Ocean strayed into the Pacific, some of the whales they met there quickly changed their tunes – singing the new whales’ songs within three short years. Some scientists are even tempted to speculate that a universal music awaits discovery.