True genetic distance may be much greater than the observed recombination frequency.Which is not an explanation of this phenomenon?

A) The genes are far apart.
B) Two crossover events may not produce recombinant chromosomes.
C) Four crossover events may not produce recombinant chromosomes.
D) Interference with 2 genes that are tightly linked affects the recombination frequency.
E) A double crossover contributes to the average number of exchanges on a chromosome.