Why Do We Think That Male Neanderthals Mated with Non-African

Why do we think that male Neanderthals mated with non-African ancestral Homo sapiens?

A) Because Neanderthal mtDNA sequences are present in the human gene pool, and Neanderthal nuclear DNA sequences are not.
B) Because neither Neanderthal mtDNA sequences nor nuclear DNA sequences are present in the modern human gene pool.
C) Because Neanderthal nuclear DNA sequences are present in the human gene pool, and Neanderthal mtDNA sequences are not.
D) Because both Neanderthal mtDNA sequences and nuclear DNA sequences are present in the modern human gene pool.