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In a popular sense, "insect" usually means the familiar pests or disease carriers. Many insects,
however, are beneficial
from a human viewpoint; they pollinate plants, produce useful substances,
control pest insects, act as scavengers, and serve as food for other. Furthermore, insects are valuable
objects of study in elucidating many aspects of biology. Much of our knowledge of genetics has been
gained from fruit fly experiments and of population biology from flour beetle studies.
Insects are
often used in investigations of hormonal action, nerve and sense organ function, and many other
physiological processes as well.
223- The passage is mainly about ............... .
A)
the benefits of insects, contrary to the negative assumptions about them
B) the methods to get rid of pests in farming
C) the importance of insects in
food production
D) a new type of insect employed in genetics
E) the relationship between insects and physiological processes
224- All the following benefits of insects are referred to by the author except the fact that they
............... .
A) help to
eradicate harmful insects
B) are eaten by other insects
C) are used in hormonal experiments
D) eat the remains of plants and animals
E) are believed
to have curative powers
225- Insects are regarded as valuable in biology because ................. .
A) scientists have grown used to working with them
B) they enlighten many dark sides in this field
C) they have many similarities with mankind
D) people consider
them to be good-natured
E) of their low cost and simplicity
Mars is the fourth planet in order of distance from the Sun and seventh in order of diminishing size
and mass. It orbits the Sun once in 687 Earth days and spins on its axis once every 24 hours and 37
minutes. Owing to the relatively large irregularity of its orbital ellipse, the distance between Mars and
the Sun varies from 206.6 million to 249.2 million km. Mars completes a single orbit in roughly the
time in which the Earth completes two. At its closest approach, Mars is less than 56 million km from
the Earth, but it recedes to almost 400 million km. Most Earth-based observations of Mars are best
made when the planet is in the opposite direction
in the sky to the Sun, allowing all-night viewing
when Mars is closest to the Earth.
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