Facing the parents' doubts about the formaldehyde exceeding the standard in the classroom that has been renovated for two months in a primary school, the principal of the elementary school responded: "I have visited all the classrooms one by one, and did not smell any odor, so the formaldehyde did not exceed the standard. ". Which of the following, if true, would best refute the principal's certification? ['Different people have different feelings about the taste.', 'More than three months after the completion of the decoration of a new house, formal inspections have shown that formaldehyde still exceeds the standard.', 'Even if the room has no odor after decoration, there may be a possibility of formaldehyde exceeding the standard within a few months after decoration.', 'Formaldehyde is a colorless and odorless gas. You cannot judge whether the formaldehyde exceeds the standard by the taste of the room.']