求助两道gwd~~~

The Earth’s rivers constantly carry dissolved salts into its oceans.  Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth’s oceans can be accurately estimated.

Which of the following is an assumption on which the argument depends?

A.    The quantityes of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.

B.    At any given time, all the Earth’s rivers have about the same salt levels.

C.    There are salts that leach into the Earth’s oceans directly from the ocean floor.

D.    There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.

E.     None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

GWD的题，给的答案是A，可是觉得E貌似也挺有道理的，想听听NN们的意见~~~

In general, jobs are harder to get in times of economic recession because many businesses cut back operations.  However, any future recessions in Vargonia will probably not reduce the availability of teaching jobs at government-funded schools.  This is because Vargonia has just introduced a legal requirement that education in government-funded schools be available, free of charge, to all Vargonian children regardless of the state of the economy, and that current student-teacher ratios not be exceeded.

Which of the following, if true, most strengthens the argument?

A.    The current student-teacher ratio at Vargonia’s government-funded schools is higher than it was during the most recent period of economic recession.

B.    During recent periods when the Vargonian economy has been strong, almost 25 percent of Vargonian children have attended privately funded schools, many of which charge substantial fees.

C.    Nearly 20 percent more teachers are currently employed in Vargonia’s government-funded schools than had been employed in those schools in the period before the last economic recession.

D.    Teachers in Vargonia’s government-funded schools are well paid relative to teachers in most privately funded schools in Vargonia, many of which rely heavily on part-time teachers.

E.     During the last economic recession in Vargonia, the government permanently closed a number of the schools that it had funded.

  这个给的答案是B,可是没有想明白。。。