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داوطلبان عزیز آزمون MSRT

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The Sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its
center that convert hydrogen to helium. The Sun has existed in its present state for about 4
billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the Sun’s life will be
like. About 5 billion years from now, the core of the Sun will shrink and become hotter. The
surface temperature will fall. The higher temperature of the center will increase the rate of
thermonuclear reactions. The outer regions of the Sun will expand approximately 35 million
miles, which is about the distance to Mercury. The Sun will then be a red giant star.
Temperatures on the Earth will become too hot for life to exist.
Once the Sun has used up its thermonuclear energy as a red giant, it will begin to shrink.
After it shrinks to the size of the Earth, it will become a white dwarf star. The Sun may throw
off huge amounts of gases in violent eruptions called nova explosions as it changes from a red
giant to a white dwarf.
After billions of years as a white dwarf, the Sun will have used up all its fuel and will
have lost its heat. Such a star is called a black dwarf. After the sun has become a black dwarf,
the Earth will be dark and cold. If any atmosphere remains there it will have frozen onto the
Earth’s surface.

2

Sea otters dwell in the North Pacific. They are the largest of the mustelids, a group that
also includes freshwater otters, weasels, and badgers. They are from 4 to 5 feet long and most
weigh from 60 to 85 pounds. Large males may weigh 100 pounds or more.
Unlike most marine mammals, such as seals or dolphins, sea otters lack a layer of
blubber, and therefore have to eat up to 30 percent of their body weight a day in clams, crabs,
fish, octopus, squids, and other delicacies to maintain body heat. Their voracious appetites do
not create food shortages, however, because they are picky eaters, each animal preferring only a
few food types. Thus no single type of food source is exhausted. Sea otters play an important
environmental role by protecting forests of seaweed called kelp, which provide shelter and
nutrients to many species. Certain sea otters feast on invertebrates, like sea urchins and
abalones, that destroy kelp.
Sea otters eat and sleep while floating on their backs, often on masses of kelp. They
seldom come on shore. Sea otters keep warm by means of their luxuriant double-layered fur, the
densest among animals. The soft outer fur forms a protective cover that keeps the fine underfur
dry. One square inch of underfur contains up to one million hairs. Unfortunately, this essential
feature almost led to their extinction, as commercial hunters drastically reduced their numbers.
Under government protection, the sea otter population has recovered. However,
occasionally unfortunate events have damaged the sea otter population. For example, in 1989,
up to 5,000 sea otters perished when the Exxon Valdez spilled oil in Prince William Sound,
Alaska.

3-

Glass is a remarkable substance made from the simplest raw materials. It can be
colored or colorless, monochrome or polychrome, transparent, translucent, or opaque.
It is lightweight impermeable to liquids, readily cleaned and reused, durable yet
fragile, and often very beautiful Glass can be decorated in multiple ways and its
optical properties are exceptional. In all its myriad forms - as table ware, containers,
in architecture and design - glass represents a major achievement in the history of
technological developments.

Since the Bronze Age about 3,000 B.C., glass lias been used for making various
kinds of objects. It was first made from a mixture of silica, line and an alkali such as
soda or potash, and these remained the basic ingredients of glass until the development
of lead glass in the seventeenth century. When heated, the mixture becomes soft and
malleable and can be formed by various techniques into a vast array of shapes and
sizes. The homogeneous mass thus formed by melting then cools to create glass, but in
contrast to most materials formed in this way (metals, for instance), glass lacks the
crystalline structure normally associated with solids, and instead retains the random
molecular structure of a liquid. In effect, as molten glass cools, it progressively stiffens
until rigid, but does so without setting up a network of interlocking crystals customarily
associated with that process. This is why glass shatters so easily when
dealt a blow. Why glass deteriorates over time, especially when exposed to moisture,
and why glassware must be slowly reheated and uniformly cooled after manufacture to
release internal stresses induced by uneven cooling.
Another unusual feature of glass is the manner in which its viscosity changes as it
turns from a cold substance into a hot, ductile liquid. Unlike metals that flow or
"freeze" at specific temperatures glass progressively softens as the temperature rises,
going through varying stages of malleability until it flows like a thick syrup. Each stage
of malleability allows the glass to be manipulated into various forms, by different
techniques, and if suddenly cooled the object retains the shape achieved at that point.
Glass is thus amenable to a greater number of heat-forming techniques than most other
materials.
10. Why does the author list the characteristics of glass in lines 1-5?
(A) To demonstrate how glass evolved
(B) To show the versatility of glass
(C) To explain glassmaking technology
(D) To explain the purpose of each component of glass
11. The word "durable"' in hue 3 is closest in meaning to
(A) lasting
(B) delicate
(C) heavy
(D) Plain
1 2. What does the author imply about the raw materials used to make glass?
(A) They were the same for centuries.
(B) They arc liquid
(C) They are transparent
(D) They are very heavy.
13. According to the passage, how is glass that has cooled and become rigid different from most
other rigid substances?
(A) It has an interlocking crystal network.
(B) It has an unusually low melting temperature.
(C) It has varying physical properties.
(D) It has a random molecular structure.
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14. The word "customarily" in line 13 is closest in meaning to
(A) naturally
(B) necessarily
(C) usually
(D) certainly
15. The words "exposed to" in line 19 are closest in meaning to
(A) hardened by
(B) chilled with
(C) subjected to
(D) deprived of
16. What must be done to release the internal stresses that build up in glass products during
manufacture?
(A) the glass must be reheated and evenly cooled.
(B) the glass must be cooled quickly.
(C) The glass must be kept moist until cooled.
(D) The glass must be shaped to its desired form immediately
17. The word "induced" in line 21 is closest in meaning to
(A) joined
(B) missed
(C) caused
(D) lost
18. The word "it" in line 22 refers to
(A) feature
(B) glass
(C) manner
(D) viscosity
19. According to the passage, why can glass be more easily shaped into specific forms than can
metals
(A) It resists breaking when heated
(B) It has better optical properties.
(C) It retains heat while its viscosity changes.
(D) It gradually becomes softer as its temperature rises.