In the frog genus, when certain species attempt to mate with other species, embryo development is halted at various stages including zygotic segmentation, blastula formation, gastrulation, or in the final phases of embryo development. The stage at which the developing frog arrests depends on the species involved in the cross. This is an example of

a.

hybrid breakdown.

b.

hybrid sterility.

c.

hybrid inviability.

d.

sexual isolation.