直齿圆柱齿轮副正确啮合的条件是：（）。

完形填空（共20小题；每小题1.5分，满分30分）

阅读下面短文，掌握其大意，然后从各题所给的A、B、C、D四个选项中，选出最佳选项。

Tired and hungry, two boys walked painfully and difficultly into a big city on October 16, on their feet that had just carried them 300 kilometers.

For nine days they lived like old-fashioned travelers,   21   somewhere new to sleep every night as they walked from one place to another. The boys slept in tents and   22   a six-yuan daily plan. “I learned more in those nine days than I had in the last nine years,” said 17-year-old Li Zhao   23 . Li and 15-year-old Li Xuemeng  24  their journey on October 7, with three teachers from an Educational Motivation Research & Service Center. The purpose of the   25  was for the two troubled boys to develop a (an)   26   attitude to school and life.

With two  27  and some instant noodles for the first day, the five  28  mainly along the Highway 107. On the way to the big city,  29   of them visited schools and interviewed   30   people from different walks of life. Both were asked to write about what they  31   during the walk.

“ The two boys need to know about   32   life and learn to get rid of difficulties, so we   33  this program,” explained Du Junpeng.    34  they had tents, they didn’t just   35  anywhere at night. “We had to   36   on people’s kindness for shelter,” said Li Zhao, who admits he used to be self-centered and at first was    37  against the idea of the trip. But the challenge of getting rid of the   38  on the journey has changed him.

“I’m more   39   than before. And now I also believe failure is the mother of  40  ,” he said.

21. A. finding             B. hunting           C. searching                      D. inventing

22. A. lived on           B. worked on      C. carried out             D. went on

23. A. anxiously         B. luckily            C. excitedly                D. tiredly

24. A. developed         B. separated               C. controlled              D. started

25. A. study                      B. trip                C. task                       D. job

26. A. passive             B. popular           C. different                D. active

27. A. tents                B. lights              C. drinks                    D. tools

28. A. ran                  B. drove             C. walked                  D. marched

29. A. both                 B. none               C. either                    D. some

30. A. famous             B. brave              C. different                D. strange

31. A. covered            B. learned           C. heard                     D. recognized

32. A. interesting               B. real                C. hard                             D. meaningful

33. A. carried on         B. cared about     C. took over                      D. worked out

34. A. Although          B. If only            C. As though              D. Since

35. A. sleep                B. adventure        C. move                     D. tour

36. A. get                   B. depend           C. take                      D. turn

37. A. hardly              B. heavily           C. strongly                 D. secretly

38. A. wrongs             B. problems               C. difficulties             D. fears

39. A. sociable            B. particular               C. common                D. formal

40. A. success             B. victory           C. hope                      D. aim

世界环境与发展委员会在1987年将（）定义为“满足当代人的需求而又不损害子孙后代发展的需要”。

A.和谐社会

B.生态经济

C.可持续发展

D.资源有偿使用

对模拟信号的布线要注意尽量远离主电路，至少在（）以上。

条件转移指令JNE的测试条件是( )。

A．ZF=1

B．CF=0

C．ZF=0

D．CF=1

对于线性系统的动态性能指标，输出响应（）。

A.不变

B.越快越好

C.越慢越好