题目

Mrs. Green, including her husband and three children, lived in a city,    36    was very near the countryside. She worked   37    a teacher and gave music lessons at a school. Of course she was fond of _   38___            Mrs. Green had a good voice and she   39    her students classes exciting. But she had a  40     point. Some of her notes (音调) were so high that they sounded like a door which needed    41   . In order to improve her notes, she took    42   chance that she could find to practise .           As her house was not big, s在平面直角坐标系中，不等式组表示的平面区域面积是（    ）．