After a nuclear power plant accident, researchers found radioactive isotopes of iodine, tellurium, and cesium-but no heavy isotopes-in the atmosphere downwind. This material came either from spent fuel rods or from the plant' s core. Spent fuel rods never contain significant quantities of tellurium isotopes. Radioactive material ejected into the atmosphere directly from the core would include heavy isotopes. After the accident, steam, which may have been in contact with the core, was released from the plant. The core contains iodine, tellurium, and cesium isotopes, which are easily dissolved by steam. Of the following statements, which one is most strongly supported by the information above? ["The nuclear power plant's spent fuel rods were not damaged.", 'Spent fuel rods do not contain heavy isotopes in significant quantities.', "The researchers found some radioactive material from spent fuel rods as well as some material that was ejected into the atmosphere directly from the plant's core.", 'The radioactive material detected by the researchers was carried into the atmosphere by the steam that was released from the plant.']