Oceanologist: Recently an unprecedented number of dead dolphins washed ashore along the mid-Atlantic coast. In the blood of over half of the dolphins, marine biologists discovered a brevotoxin that had been emitted by the alga Ptychodiscus brevis, in what is known as a red tide. Additionally, polychlorinated biphenyls (PCB), a toxic industrial compound, was also found in the dolphin's blood. A reasonable conclusion, and indeed one many have drawn, is that the dolphins were simply victims of the brevotoxin. Nonetheless, brevotoxins, by themselves, are not lethal to dolphins, though they do tax the dolphins system. Furthermore, most dolphins have some accumulated brevotoxins in their blood without suffering any ill health effects. Therefore, the brevotoxins alone cannot explain the mass beaching of dead dolphins.
Which of the following, if true, does most to help explain the oceanologist's doubt that the brevotoxins were the primary cause of the dolphins washing upon shore?
【选项】Shortly before the dolphins washed ashore, a major oil spill not only caused algae to release brevotoxins but also released an array of deleterious industrial pollutants, including PCB.
选项是否正确？