当防烟楼梯间及其合用前室分别设置机械加压送风系统时，各处空气压力值应为( )

在同一个办公建筑的标准层，采用定新风比全空气系统与采用新风加风机盘管空调系统相比，前者需要的以下哪一项更大？(...

单项选择题在同一个办公建筑的标准层，采用定新风比全空气系统与采用新风加风机盘管空调系统相比，前者需要的以下哪一项更大？( )

关于光敏晶体管的使用，描述正确的有A、光敏二极管在使用时应反向偏置 B、光敏三极管在无光照时，输出电流很小，有...

多项选择题关于光敏晶体管的使用，描述正确的有
A、光敏二极管在使用时应反向偏置
B、光敏三极管在无光照时，输出电流很小，有光照时，输出较大电流
C、一种光敏晶体管只对一定波长范围的入射光敏感
D、光敏二极管检测光照的线性度较好 
E、温度对亮电流小，对暗电流影响显著

根据下面资料，回答21-35题Sometimes I feel that being the mother o...

单项选择题根据下面资料，回答21-35题
Sometimes I feel that being the mother of three small children is like operating a large circus(马戏团)．21afternoon last week, my three sons playing peacefully in the back yard ( 院子),22the ball from one to another．I jumped at the chance to talk to one of my friends23the phone, but before I24to the phone, I could tell the boys had begun to quarrel with each other about something．I rushed out to25peace,but before I got there Charles had26a rock at Mark,and hit him in the eye．By the time I got to the back yard,they had begun to27about this．Even David,the oldest boy,who won' t usually fight with anybody about28,was involved(卷入) First,!29them stop fighting, and then ! examined Mark' s eye．I decided that it wasn' t going to develop into a black eye, but I felt that they should30at least a little for31they had done．"I' m going to32to your father about this when he comes home tonight,"I said．"He and I will think of how to punish you．"Things were33quiet after that for about half an hour, and then Charles34a glass in the kitchen,and at almost the same35,Mark fell out of the apple tree．
第（33）题答案