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托福试题_阅读理解模拟题及答案4

中华考试网   2016-12-20   【

  Bloodhounds are biologically adapted to trailing their prey. The process by which

  the nose recognizes an odor is not fully understood, but there are apparently specific

  receptor sites for specific odors. In one explanation, recognition occurs when a scent

  molecule fits into its corresponding receptor site, like a key into a lock, causing a

  (Line5) mechanical or chemical change in the cell. Bloodhounds apparently have denser

  concentrations of receptor sites tuned to human scents.

  When a bloodhound trails a human being, what does it actually smell? The human

  body, which consists of about 60 trillion living cells, sheds exposed skin at a rate of 50

  million cells a day. So even a trail that has been dispersed by breezes may still seem

  (Line10) rich to a bloodhound. The body also produces about 31 to 50 ounces of sweat a day.

  Neither this fluid nor the shed skin cells have much odor by themselves, but the

  bacteria working on both substances is another matter. One microbiologist estimates

  the resident bacteria population of a clean square centimeter of skin on the human

  shoulder at "multiples of a million." As they go about their daily business breaking

  (Line15) down lipids, or fatty substances, on the skin, these bacteria release volatile

  substances that usually strike the bloodhound's nose as an entire constellation of

  distinctive scents.

  45. What does the passage mainly discuss?

  (A) Why people choose bloodhounds for

  household pets

  (B) How a bloodhound's sense of smell works

  (C) How humans compensate for an

  underdeveloped sense of smell

  (D) The way in which bacteria work on skin cells

  and body sweat

  46. The author compares a scent molecule with a

  (A) key

  (B) lock

  (C) cell

  (D) bloodhound

  47. In line 7, the word "it" refers to

  (A) bloodhound

  (B) human being

  (C) smell

  (D) body

  48. According to the passage, how many cells of

  skin does the human body rid itself of every day?

  (A) 60 trillion

  (B) 50 million

  (C) 1 million

  (D) Between 31 and 50

  49. In line 10, the word "rich" is used to mean that a

  trail is

  (A) paved with precious materials

  (B) a profitable business to get into

  (C) a very costly undertaking

  (D) filled with an abundance of clues

  50. Which of the following acts as a stimulus in the

  production of the human scent?

  (A) Sweat

  (B) Dead skin cells

  (C) Bacteria

  (D) Fatty substances

  参考答案:BAABDC

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