Scientists removed all viruses from a seawater sample and then measured the growth rate of the plankton population in the water. They expected the rate to increase dramatically, but the population actually got smaller. Which one of the following, if true, most helps to explain the unexpected result described above? ['Viruses in seawater help to keep the plankton population below the maximum level that the resources in the water will support.', 'Plankton and viruses in seawater compete for some of the same nutrients.', 'Plankton utilize the nutrients released by the death of organisms killed by viruses.', 'The absence of viruses can facilitate the flourishing of bacteria that sometimes damage other organisms.']