题目

如图，AD=，E是BC的中点，BE=，求线段AC和DE的长． 答案：【考点】两点间的距离． 【分析】根据线段中点的性质，可得BC的长，根据线段的和差，可得AC的长，可得关于DB的方程，根据解方程，可得DB的长，再根据线段的和差，可得答案． 【解答】解：由E是BC的中点，BE=，得 BC=2BE=2×2=4cm， AB=3×2=6cm， 由线段的和差，得 AC=AB+BC=4+6=10cm； AB=AD+DB， 即DB+DB=6， 解得The following is a mark table (分数表) about the English competition. Find some useful information to the questions below. (读下面的英语竞赛成绩单，回答后面的问题。) Items Group1 Group2 Group3 Group4 1.answer correctly 66 72 75 77 2.answer quickly 74 79 78 63 3.answer humorously (幽默地) 68 69 80 78 4.speak clearly 87 85 82 87 5.speak loudly 90 92 90 91 6.speak freely 80 82 83 84 7.have a good manner 78 75 74 78 8.co-operate (合作) well 81 64 87 84 Average (平均分) 78 77 81 80 (  ) 1. _______ co-operate best of all the groups. A. The students in Group 1              B. The students in Group 2 C. The students in Group 3              D. The students in Group 4 (  ) 2. Group 1 is thought to have spoken as _________ as Group 3. A. clearly     B. loudly       C. freely        D. quickly (  ) 3. Group 4 did worst in “________”. A. answer humorously              B. speak freely C. have a good manner              D. answer quickly (  ) 4. In “answer correctly”, Group 1 was _____ marks lower than Group 4. A. 6        B. 9         C. 11         D. 10 (  ) 5. Which of the following is NOT true? A. Group 1 did as well as Group 4 in “have a good manner”. B. All the groups of Group 3 is 3 marks more than Group 1. C. The average of Group 3 is 3 marks more than Group 1. D. Group 3 is the winner of the competition.