19. If goats are crossed with sheep, embryos will form but cease development and spontaneously abort. This is an example of
(A)a prezygotic mechanism.
(B)hybrid inviability.
(C)hybrid sterility.
(D)hybrid breakdown.
(E)spermatic behavior.

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統計： A(0), B(17), C(3), D(1), E(1) #2344912