Why Was the Fossil Evidence for Interbreeding Between Neanderthals and Homo

Why was the fossil evidence for interbreeding between Neanderthals and Homo sapiens inconclusive?

A) The fossil evidence was very scant and incomplete.
B) Fossil evidence appeared to show morphological characters intermediate between H. sapiens and H. neanderthalensis, but could not determine if that was solely due to interbreeding.
C) Many researchers argue that H. sapiens and H. neanderthalensis are the same species, so the fossil evidence is not applicable.
D) Researchers were unable to extract DNA from Neanderthal fossils.