In 1928, a Russian Plant Geneticist Crossed Cabbage (Brassica) with Radish

In 1928, a Russian plant geneticist crossed cabbage (Brassica) with radish (Raphanus) .Fusion of gametes produced mostly infertile hybrids, but a few fertile plants contained a complete set of cabbage (n = 9) and radish (n = 9) chromosomes (n = 18) .Fusion of their gametes in turn produced fertile 36-chromosome plants with cabbage-like roots and radish-like leaves.These plants could interbreed, but not with cabbage or radish ancestors.Production of this species, which can also occur naturally, is called

A) autopolyploidy.
B) allopatric speciation.
C) hybrid sterility.
D) allopolyploidy.
E) hybridization.