Many probes have been launched to Mars in order to find out if there is life on Mars. The surface of Mars was found to be acidic soil with a lot of sulfates in the detection area, which indicates the existence of volcanic activity on Mars. In addition, the detection data show that Mars soil samples also show Signs of perchlorate. Perchlorate is a compound that can serve as an energy source for Martian microorganisms. At the same time, a strange sign on the surface of Mars, reduced iron, was found to indicate that life had existed on the surface of Mars. If the following ______ items are true, they can best question the above discussion. ['On Earth, reduced iron is generally formed by microorganisms.', 'Sulfur erupted from a volcanic eruption. Sulfur dioxide was burned to generate sulfur dioxide. Sulfur dioxide met water to form sulfurous acid, which was oxidized to sulfuric acid, and sulfuric acid reacted with metals to form sulfates.', "Discovery found no liquid water on Mars' surface.", 'The chemical reaction between the iron on the planet and the organic carbon carried by the comet that hits it can produce reduced iron.']