雅思阅读模拟试题学术类(9)
2023-05-26 12:38:05 来源:中国教育在线
雅思阅读模拟试题学术类(9) 关于这个问题下面小编就来为各个考生解答下。
雅思阅读模拟试题学术类(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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