It is healthy to live around trees. Trees work as doctors and they keep us healthy.
Many scientists have studied how trees clean the air. For people in large cities, trees can be very important for their health. These days, cities are planting trees not just in parks. They are also planting trees along streets in order to help clean the air.
Some scientists also believe trees help more than just the air. Trees keep our bodies healthy as well. People in hospitals seem to do better when they can see trees from their rooms. People with trees near their homes usually take more exercise.
Scientists have also studied the healthy effects (效果) of trees on our minds. One effect of trees seems to be that they make people feel relaxed. Scientists did some research on city people in an area with few trees. After trees were planted on the street, people walked slower when going home. They said the area was much nicer.
Of course, another good effect is that doctor trees work for free!
