Which of the below is a limitation of the biological species concept?

Two organisms "supposed to be"of the same species, and both masculine, cannot breed together, so they can't be of the same species. If an organism "A" can breed with two other organisms "B" and "C", it means that "A", "B" and "C" all (appear to) belong to a single species, but not necessarily "B" and "C" must be capable of breed together, meaning that "B" and "C" belong to different species.