TOEFL Reading練習 #014 — Same Atom, Two Extremes(日本語解説)

1. A. speed
2. B. friction
3. C. assistance
4. D. persistence

1. A. diamond and graphite
2. B. carbon atoms
3. C. hardness and softness
4. D. elements and minerals

1. A. any mineral that is mined for industrial or decorative use
2. B. the extreme hardness that some forms of carbon can have
3. C. different structural arrangements of the same element that produce very different physical properties
4. D. the rigid three-dimensional network formed when carbon atoms bond to four neighbors

1. A. Diamond conducts heat away from the blade fast enough to prevent overheating
2. B. Diamond is cheaper to produce than the metals used for typical drill tips
3. C. Diamond is more attractive for use in jewelry than any other mineral
4. D. Diamond is harder than almost anything else, so it does not wear down while cutting through rock or metal

1. A. Each carbon atom bonds to only three neighbors, forming flat sheets shaped like a honeycomb
2. B. Each carbon atom bonds to four neighboring atoms in a rigid three-dimensional network
3. C. The bonds between one layer and the next are weak enough that the layers can slide across each other
4. D. The electrons between the layers are loosely held and can move freely, allowing graphite to conduct electricity

1. A. Graphite conducts electricity because the electrons between its layers can move freely, but diamond cannot conduct electricity because all of its electrons are fixed in place within rigid bonds.
2. B. Graphite conducts electricity, while diamond does not.
3. C. Diamond conducts electricity because its electrons are free to move between layers, while graphite cannot because its electrons are locked in rigid bonds.
4. D. Graphite conducts electricity only when it is compressed into layers, but diamond can never conduct electricity under any circumstance.

1. A. It would remain chemically different from diamond even under identical pressure and temperature conditions
2. B. It would form flat sheets that stack loosely, exactly as it does at the surface
3. C. Its carbon atoms could be forced into the tightly bonded three-dimensional network that defines diamond, since the same atoms can form different allotropes depending on how they are arranged
4. D. It would immediately become useless for any industrial purpose

1. A. list the different tools that contain diamond
2. B. explain why graphite is used in pencils instead of diamond
3. C. compare the price of diamond jewelry to the price of industrial tools
4. D. give a concrete example of how diamond's extreme hardness is put to practical use beyond jewelry

1. A. It restates the same rigid three-dimensional network described in paragraph 2
2. B. It describes an atomic arrangement opposite to the one in paragraph 2, which produces properties opposite to diamond's
3. C. It provides more evidence that supports the exact same properties described in paragraph 2
4. D. It explains how the underground formation conditions described in paragraph 4 apply to diamond

1. A. Square A
2. B. Square B
3. C. Square C
4. D. Square D

Diamond Graphite

1. A. Each carbon atom bonds to four neighboring atoms in a rigid three-dimensional network
2. B. Ranks 10, the highest possible score, on the Mohs hardness scale
3. C. Is often used to tip industrial drills and saws
4. D. Each carbon atom bonds to only three neighbors, forming flat sheets that stack loosely on top of each other
5. E. Conducts electricity because loosely held electrons can move freely between its layers
6. F. Forms only when carbon combines with oxygen at high temperatures
7. G. Melts at a lower temperature than most other minerals