请求evluate题目的解题思路

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

选a

题目最后说因此知道从seawater里提取uranium的价格变低了那么用这种方法取得uranium好像在商业上不可行，我觉得这个因此那么很矛盾的
。不知道这种题目该怎么做呢。

第二题：

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.

 选d

对此类题目真的毫无头绪，需要大家的帮助谢谢，希望大家把自己的理解写下，我也去翻翻og上相关的题目和它的解释。