In the face of parents' doubts about the excessive formaldehyde in the classroom decorated for two months in a primary school, the principal of the primary school responded: I have been to all the classrooms one by one and didn't smell any peculiar smell, so the formaldehyde doesn't exceed the standard.
 Formaldehyde is a colorless and tasteless gas. It is impossible to judge whether formaldehyde exceeds the standard by the taste of the room can best refute the certification of the primary school principal.