Investigators of the fire at the Shelburne factory have determined that the traces of gasoline on the property resulted from a leaking truck and were not, as they previously thought, the work of an arsonist. The investigators had originally maintained that the fire could have resulted from arson, faulty wiring, or an explosion of factory equipment. However, in light of all the evidence collected so far, they are currently exploring only the faulty-wiring theory. The statements above provide the most support for which one of the following inferences? ['The gasoline leaking from the truck did not help to cause the truck to explode.', 'The investigators believe that the fire was not caused by an explosion of factory equipment.', 'The investigators have until now seriously explored only the possibility that the fire resulted from arson.', 'The investigators have physical evidence that the wiring in the Shelburne factory was faulty.']