Humans Have 23 Pairs of Chromosomes, and Chimps Have 24

Humans have 23 pairs of chromosomes, and chimps have 24 pairs of chromosomes. What is the most likely explanation for these differences in human and chimp genomes?

A) The common ancestor of humans and chimps had 24 pairs of chromosomes. During human evolution, two human chromosomes fused end to end.
B) In the evolution of chimps, new adaptations resulted from additional chromosomal material.
C) At some point in evolution, human and chimp ancestors reproduced with each other.
D) Errors in mitosis resulted in an additional pair of chromosomes in chimps.