雅思閱讀模擬試題學術(shù)類（9）

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雅思閱讀模擬試題學術(shù)類（9）

READING PASSAGE 3

You should spend about 20 minutes on Questions 27–40, which are based on Reading

Passage 3 below.

HELIUM’S FUTURE UP IN THE AIR

A In recent years we have all been exposed to dire media reports concerning the

impending demise of global coal and oil reserves, but the depletion of another key nonrenewable resource continues without receiving much press at all. Helium – an inert,

odourless, monatomic element known to lay people as the substance that makes

balloons float and voices squeak when inhaled – could be gone from this planet within a

generation.

B Helium itself is not rare; there is actually a plentiful supply of it in the cosmos. In

fact, 24 per cent of our galaxy’s elemental mass consists of helium, which makes it the

second most abundant element in our universe. Because of its lightness, however, most

helium vanished from our own planet many years ago. Consequently, only a miniscule

proportion – 0.00052%, to be exact – remains in earth’s atmosphere. Helium is the byproduct of millennia of radioactive decay from the elements thorium and uranium. The

helium is mostly trapped in subterranean natural gas bunkers and commercially

extracted through a method known as fractional distillation.

C The loss of helium on Earth would affect society greatly. Defying the perception

of it as a novelty substance for parties and gimmicks, the element actually has many

vital applications in society. Probably the most well known commercial usage is in

airships and blimps (non-flammable helium replaced hydrogen as the lifting gas du jour

after the Hindenburg catastrophe in 1932, during which an airship burst into flames and

crashed to the ground killing some passengers and crew). But helium is also

instrumental in deep-sea diving, where it is blended with nitrogen to mitigate the dangers

of inhaling ordinary air under high pressure; as a cleaning agent for rocket engines; and,

in its most prevalent use, as a coolant for superconducting magnets in hospital MRI

(magnetic resonance imaging) scanners.

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