Biologists found that off the northeast coast of a certain country the P-plankton population has recently dropped 10 percent. Additionally, fish species X, Y, and Z are beginning to show extraordinarily high death rates in the region. Since these species of fish are known to sometimes eat P-plankton, biologists believe the two phenomena are connected, but the exact nature of the connection is unknown. No other species in the ecosystem appear to be affected. Which one of the following, if true, most helps to explain the biologists' findings? ['Global warming has changed the climatic conditions of the ocean all along the northeast coast of the country.', 'A powerful toxin in the water is killing off P-plankton by inhibiting their production of a chemical they use in reproduction.', 'Fish species X, Y, and Z are all experiencing widespread starvation within the affected region, and the loss of P-plankton is driving their death rates up even higher.', 'A new strain of bacteria is attacking P-plankton by destroying their cell walls and is attacking the respiratory systems of fish species X, Y, and Z.']