The main cause of a heart attack is not exercise or stress -- it's air pollution, according to a study published in The Lancetthis month. Researchers found spending time in traffic, whether as a driver or a pedestrian , tops the list of risk factors that bring on a heart attack. Jon Ayres, professor of environmental and respiratory  medicine at the University of Birmingham, says, "Air pollution is not only linked to strokes, heart attacks and cancer -- it has a deep effect on those with existing respiratory conditions." So how can you avoid the damage? We asked the experts for their tips. TAKE TO THE SIDE STREETS Avoid main roads. These have the highest number of vehicles and also more traffic jams, which tend to run on diesel . Diesel engines emit  tiny particles  that reach the lungs most easily. Choose side streets, pavements, parks and avenues lined with trees.  BUY SOME HOUSEPLANTS We spend 90 percent of our time inside, but studies by the U.S. Environmental Protection Agency have found that pollution levels can be two to five times higher indoors than outside. Objects such as synthetic  carpets, TV screens can emit chemicals called volatile organic compounds (VOC,), which have been linked to diseases such as cancer. Researchers at Curtin University in Perth,  Australia, found an increase in asthma  risk among children under three who    had high VOC levels in their homes. Therefore, the application of air fresheners and houseplants can keep the circulation of the air and absorb the pollutants. For people's health, which of the following should NOT be chosen, according to the passage?
Side streets. Main streets. Pavements. Parks.