听力原文： The University of California at Davis has government experiments with chemicals to get a bigger crop each year. But they haven't paid enough attention to necessary safety measures. In 1964 or 1965, an airplane was spraying chemicals over the fields. Flying low, the wheels of the plane were caught on the fence wire. The pilot got out, dusted himself off, and drank some water from a nearby pond. Then he died. The nurses and doctors got terribly sick too because of the chemicals he had on his body. A little girl was playing around a sprayer. She stuck her tongue on it and she died immediately. These chemicals affect the farm worker through the lungs. He breathes them in. Nobody looks into the cause at all. They just was the he is sick. Why did the plane fall to the ground?