In people's impression, bio-fuel is a renewable green energy. The latest research results overturn people's traditional impression. Researchers found that bio-fuel may be converted into acetaldehyde due to incomplete combustion, which will pollute the air. This pollution will lead to 1400 early deaths in country M every year. 
Scientists predict that as research progresses, acetaldehyde will no longer be produced by new biofuels in five years.
 some medical institution personnel in country M believe that the promotion of bio-fuels should be suspended and its use should be limited at this stage.