What can the reader infer based on the underlined detail of the excerpt from "Lincoln the Great"?

"For a country said to be uninterested in its past, this would seem to be a giant exception to the rule. There are few if any decisive new facts remaining to be unearthed. There continue to be bands of Lincoln assassination enthusiasts who find it irresistible to speculate about what did or did not happen those fateful days in the spring of 1865. But they don't explain the passionate interest in the man."

The reader can infer that:
A. Experts recently unearthed some of Lincoln's possessions to learn more about him.
B. Historians have decided not to continue research on Lincoln.
C. Lincoln's life and background aren't particularly interesting.
D. A great deal of research on Lincoln has already been done.