题目

若  ，  满足  ，则  的最大值为（        ） A.0          B.3           C.4            D.5 答案：C 【解析】 2x+y=4,故选C.I rise in the east. I send my light into your room,and tell you it is time 1    . I send my light here and there. I shine on the trees, the houses, the hills and the water;and I make everything 2    beautiful. I give you light and heat. I make the fruit and rice ripe. I am high up in the 3    . Sometimes I hide my head 4    a thin cloud, and then you may look at me. I travel in the sky. I never stop,and I am never tired. But in fact it is the earth that is 5   all the time.The earth is big. It is a big,round ball. There are rocks on the earth. There is soil on the earth. There is water on the earth. 6    the people on the earth? Will they 7    the earth? Jump. You come down to earth. Jump up 8    . You always come down to earth. Snow comes down. Leaves come down. Rain comes down. The ball comes down. The earth 9    things down. The pull of 10    is the gravity(吸引力，引力) .Gravity holds the soil to the earth. It holds the water and the air. Gravity holds people to the earth,too. Gravity holds you to the earth.(   ) 1.A. to go to bed   B. having sports  C.to get up   D. wash clothes(   ) 2.A. seem   B. shine   C. appear   D. look(   ) 3. A. sea   B. clouds   C. mountain   D. sky(   ) 4. A. in front of   B. before   C. behind   D. near(   ) 5. A. bright   B. lying   C. moved   D. traveling(   ) 6. A. Enjoy   B. Look   C. See   D. Know(   ) 7. A. fall off   B. sink down   C. lose heart   D. open out(   ) 8. A. too   B. either   C. again   D. any longer(   ) 9. A. pulls   B. pushes   C. brings   D. catches(   ) 10.A. the sun   B. the earth   C. the moon   D. the space