In a follow up to Alfred Sturtevant's studies on recombination in the fruit fly, Seymour Benzer used complementation studies of bacteriophage mutants to verify where recombination happens along a chromosome. Which of the following best explains his conclusions?

A. A gene is an indivisible unit thus recombination occurs among neighboring genes

B. Recombination happens at the level of the nucleotide and can therefore occur within a gene itself

C. The process of recombination is restricted to the centromere of each chromosome thus entire arms are smallest units that are exchanged during crossing over. 

D. Recombination is limited to the exchange of material among the nuclear genome and the  mitochondrial genome.