求助prep上的一道逻辑题

各位考友，做题时在C/E之间徘徊最终还是选错了，正确答案是C。可是如何排除E呢，比较迷惑中？？

Which of the following most logically completes the argument?

United States manufacturers currently produce most of the world's solar-power generators--most of which are exported to Europe.  However, European manufacturers are emerging and probably will ultimately capture much of the European market.  The United States government is funding initiatives intended to encourage use of solar power within the United States.  If these initiatives succeed in increasing the demand for solar-power generators in the United States, United States manufacturers will probably maintain significant production levels, since __________.

(A) some United States manufacturers have been substantially increasing their output over the last several years

(B) the efficiency of solar-power generators in converting energy from the Sun into electric power is not improving as fast as it once did

(C) just as European manufacturers enjoy certain competitive advantages in Europe, so do United States manufacturers in the United States

(D) European governments are currently undertaking initiatives to stimulate the use of solar power within Europe

(E) the current market for solar-power generators in the United States is very limited

还有一题，正确答案为A，请问C为什么不对呢？最近总是逻辑错的多，以前不是这样的，郁闷中。。。

Most of the world's supply of uranium currently comes from mines.  It is possible to extract uranium from seawater, but the cost of doing so is greater than the price that uranium fetches on the world market.  Therefore, until the cost of extracting uranium from seawater can somehow be reduced, this method of obtaining uranium is unlikely to be commercially viable.

Which of the following would it be most useful to determine in evaluating the argument?

(A) Whether the uranium in deposits on land is rapidly being depleted

(B) Whether most uranium is used near where it is mined

(C) Whether there are any technological advances that show promise of reducing the cost of extracting uranium from seawater

(D) Whether the total amount of uranium in seawater is significantly greater than the total amount of uranium on land

(E) Whether uranium can be extracted from freshwater at a cost similar to the cost of extracting it from seawater

再加一道题，我怎么总错evaluate这类题呢，郁闷死了。。。

Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas.  In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide.  Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Which of the following, if true, would it be most important to take into account in evaluating the result?

(A) The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas.

(B) At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.

(C) The urban class conducting the experiment was larger than the rural class conducting the experiment.

(D) Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside.

(E) Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school's greenhouse were changed more frequently than were those at the rural school.