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 quantities 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

Pls give ans with reasoning

B for me.

yeap i too went for B,but the OA is A/E,iam not sure

i think its E.

if the salts are used up by biological activity in the ocean, then a correct estimate of the amount of salt in the ocean cannot be made ('coz some of it would have been used up) and hence, a correct estimate of the oceans' age cannot be made.

but i am not sure why A is wrong - it can also be right by the same reasoning as E.

the correct answer is "E" only.