题目

如图，在梯形ABCD中，AD∥BC，AD＝6，BC＝16，E是BC的中点.点P以每秒1个单位长度的速度从点A出发，沿AD向点D运动；点Q同时以每秒2个单位长度的速度从点C出发，沿CB向点B运动.点P停止运动时，点Q也随之停止运动.当运动时间t＝             秒时，以点P，Q，E，D为顶点的四边形是平行四边形.   答案：2或解析:略 I teach biology at UNLV three times per week. Last Monday, at the beginning of class, I cheerfully asked my  21  how their weekend had been. One young man said that his weekend had not been so  22 . He had his wisdom teeth removed. Then he went on to ask me why I always seemed to be so  23 .        His question  24  me of something I’d read somewhere before: “Every morning when you get up, you have a  25  about how you want to deal with life that day,” I said. “I choose to be cheerful.” “Let me give you an example,”I continued,  26 all sixty students in the class. “In  27  to teaching here at UNLV, I also teach out at a  28  in Henderson, 17 miles down the highway from where I live. One day a few weeks ago I drove those 17 miles to Henderson. I  29   the highway and turned onto College Drive. I only had to drive another quarter mile down the road to the college. But just then my car  30 . I tried to start it again, but the 31  wouldn’t work.  32  I turned my flashers on, took my books, and  33  down the road to the college.” “As soon as I got there, I called and  34  for a tow truck to meet me at my car after  35 . The secretary there asked me what had happened. ‘This is my  36  day.’ ” I replied, smiling. She was 37 . “What do you mean?” “My car could have broken down anywhere along the highway. It didn’t.” I replied. “ 38 , it broke down in the perfect place: off the highway, 39  walking distance of here. I’m still able to teach my class, and I’ve been able to arrange for the tow truck to meet me after class. If my car was meant to break down today, it couldn’t have been arranged in a more convenient 40 .” I ended my story. In spite of the early hour, no one in my class seemed to be asleep. Somehow, my story had touched them. 21. A.schoolmates         B. children            C. teachers           D.students 22. A. had                    B. good            C. sad                          D.free 23. A. cheerful             B. grateful            C. hopeful                    D. thankful 24. A. informed            B.told                C. reminded                 D. warned 25. A. decision            B. choice             C. preference                      D. judgment 26. A. showing            B. demanding        C. addressing                   D. commanding 27. A. contribution       B. devotion      C. application           D. addition 28. A. school            B. college         C. university            D. institute 29. A. exited               B. found               C. crossed                    D. entered 30. A. broke              B. died             C. ended                    D. finished 31. A. instrument      B. wheel          C. light              D. engine 32. A. But              B. And             C. So                    D. Or 33. A. marched        B. drove              C. rode                D. followed 34. A. prepared            B. looked          C. waited                  D. arranged 35. A. class                   B. work               C. study                 D. lunch 36. A. usual                  B. unusual            C. unlucky                    D. lucky 37. A. astonished                B. excited            C. puzzled                 D. pleased 38. A. Anyway            B. Instead            C. Also                  D. Still 39. A. within             B. beyond            C. without                  D. along 40. A. order                       B. need                C. way                D. situation