新GRE阅读理解36套每日讨论--56（群178674184）

普渡哥

       Echolocating bats emit sounds in patterns characteristic
       of each species that contain both frequency-
       modulated (FM) and constant-frequency (CF) signals.
       The broadband FM signals and the narrowband
5      CF signals travel out to a target, reflect from it, and
       return to the hunting bat. In this process of transmission
       and reflection, the sounds are changed, and the changes
       in the echoes enable the bat to perceive features
       of the target.
10   The FM signals report information about target
       characteristics that modify the timing and the fine
       frequency structure, or spectrum, of echoes—for example,
       the target‘s size, shape, texture, surface structure,
       and direction in space. Because of their narrow
15    bandwidth, CF signals portray only the target‘s presence
       and, in the case of some bat species, its motion relative
       to the bat‘s. Responding to changes in the CF echo‘s frequency,
       bats of some species correct in flight for the direction and
       velocity of their moving prey.
(150 words)


8. According to the passage, the information provided
to the bat by CF echoes differs from that provided
by FM echoes in which of the following ways?
(A) Only CF echoes alert the bat to moving targets.
(B) Only CF echoes identify the range of widely
spaced targets.
(C) Only CF echoes report the target‘s presence to
the bat.
(D) In some species, CF echoes enable the bat to
judge whether it is closing in on its target.
(E) In some species, CF echoes enable the bat to
discriminate the size of its target and the
direction in which the target is moving.


9. Which of the following best describes the organization
of the passage?
(A) A fact is stated, a process is outlined, and
specific details of the process are described.
(B) A fact is stated, and examples suggesting that
a distinction needs correction are considered.
(C) A fact is stated, a theory is presented to explain
that fact, and additional facts are introduced
to validate the theory.
(D) A fact is stated, and two theories are compared
in light of their explanations of this fact.
(E) A fact is stated, a process is described, and
examples of still another process are
illustrated in detail.

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