Map Units on a Linkage Map Cannot Be Relied Upon

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

A) The frequency of crossing over varies along the length of the chromosome.
B) The relationship between recombination frequency and map units is different in every individual.
C) Physical distances between genes change during the course of the cell cycle.
D) The gene order on the chromosomes is slightly different in every individual.
E) Linkage map distances are identical between males and females.