Recent research indicates that mercury levels in the bodies

Recent research indicates that mercury levels in the bodies of saltwater fish are higher now than they were a hundred years ago. Mercury from the fish accumulates in the base of the feathers of seabirds that eat saltwater fish. Feathers taken from seabirds stuffed and preserved in the 1900s were found to contain only half as much mercury as do feathers recently taken from living birds of the same species.

The argument depends on the assumption that

A) The number of sources of pollutants in 1900s was much lower than it is now.
B) The quantity of mercury found in the body of a saltwater fish depends on the amount of pollution in the ocean habitat of the fish.
C) The same techniques used today were used to stuff and preserve birds in the 1900s.
D) The process used to preserve birds in the 1900s did not substantially decrease the amount of mercury in the birds’ feathers.
E) The Proportion of saltwater fish in the diet of seabirds has remained the same since the 1900s.

Source - Crackverbal