Which statement about polyploidy in plants is true?

A. Polyploid plants are usually less vigorous than diploid plants of the same species.
B. Tetraploid and diploid plants of a given species can mate to produce viable triploid offspring.
C. Allopolyploids are hybrid plants that result from the mating of two closely related species.
D. Tetraploid plants can mate with other tetraploid plants of the same species, but not with themselves.
E. Polyploidy is rare in plants.