若不等式组
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不等式组
将前三个不等式所表示的平面区域，x-y≥0 2x+y≤2 y≥0 x+y≤a
三个顶点分别为（0，0），（1，0），(
，2 3
)，2 3
第四个不等式x+y≤a，
表示的是斜率为-1的直线的下方，
如图，只有当直线x+y=a和直线2x+y=2的交点介于点A，B之间时，
不等式组所表示的区域才是四边形，此时1＜a＜
．4 3
故选C．
用方框中所给单词的适当形式填空，使短文通顺、正确、连贯(每个单词限用一次)。
As the afternoon was hot. I did my work in the morning. I 63 to get up at 6:30 and take a walk in the garden for half an hour. After breakfast, I began reading English and Chinese and did some 64 in math, It took me three hours or65 . I worked quite 66and made good progress. I spent the afternoon outside. I went to swim and it was 67 . I would not go home until it was about five or six o’clock. Sometimes a friend of mine would come to see me and we would spend some hours 68 to music. In this way I spent my vacation slowly. And I not only studied well but also became a good 69 . now I am in good 70 and high spirits. |