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Plankton generally thrive in areas of the ocean with sufficient concentrations of certain nitrogen compounds near the surface where plankton live. Nevertheless, some areas, though rich in these nitrogen compounds, have few plankton. These areas have particularly low concentrations of iron, and oceanographers hypothesize that this shortage of iron prevents plankton from thriving. However, an experimental release of iron compounds into one such area failed to produce a thriving plankton population, even though local iron concentrations increased immediately.
Which of the following, if true, argues most strongly against concluding, on the basis of the information above, that the oceanographers’ hypothesis is false? D
A: Not all of the nitrogen compounds that are sometimes found in relatively high concentrations in the oceans are nutrients for plankton.
B: Certain areas of the ocean support an abundance of plankton despite having particularly low concentrations of iron.
C: The release of the iron compounds did not increase the supply of nitrogen compounds in the area.
D: A few days after the iron compounds were released, ocean currents displaced the iron-rich water from the surface.
E: The iron compounds released into the area occur naturally in areas of the ocean where plankton thrive.
In recent years, networks of fiber-optic cable have been replacing electrical wire for transmitting telecommunications signals. Signals running through fiber-optic cables deteriorate, and so the signals must be run through a piece of equipment called a regenerator before being transmitted father. Light-Line is the leading manufacturer of signal regenerators. Therefore, Light-line is one of the companies that will most benefit if new long-distance fiber-optic telecommunications networks are constructed.
Which of the following, if true, casts the most doubt on the prediction about light-ling’s prospects? E
A: Telecommunications signals sent along electrical wires can travel much farther than signals transmitted through fiber-optic before needing to be regenerated.
B: Expanding its production of regenerators will require Light-line to spend proportionately more on labor and materials.
C: The volume of signals that a fiber-optic cable can carry is several thousand times greater than the volume that can be carried by an electrical wire of similar size.
D: There are technologies that enable telecommunications signals to be transmitted without either wire or fiber-optic cable.
E: Several manufacturers are developing regenerator technologies that will allow signals to be transmitted many times farther than at present before requiring regeneration.
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发表于 2009-3-22 21:23:00
