Which of the following statements correctly explains the fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment?
A) None of the traits obeyed the law of segregation.
B) The diploid number of chromosomes in the pea plants was seven.
C) All of the genes controlling the traits had only two different alleles.
D) All of the genes controlling the traits were on different chromosomes.