根据下面资料，回答21-35题
In the past, I always thought that being a teacher was an easy job. But I changed my（21）when I became a part-time teacher. About four years ago, Richard asked me（22）I could help teach his students how to make a website about themselves.
I（23）because computer is what I do well and I didn′ t think teaching computer would bethat（24）.
But when 1 taught Richard′ s class, some of the students（25）with their friends while I was explaining how to do something. At first I just got angry with them,（26）Richard taught me to think why they were doing this. He said that if he was（27）a lesson and the students were not lis-tening, then he was angry with（28）for not making the lesson clear or interesting for them. I told him that I didn′ t（29）his idea. He then asked me if l had ever（30）the same thing. That made me stop. Of course I had !
If any of my past teachers are（31）this, I want to say sorry if I sometimes played around in the class（32）you were teaching. I didn′ t think how that would make you feel. I promise I will do my best to be a good（33）in the future. Please help us when we don′t understand and most（34）, don′ t be quick to be angry when we fail.（35）of us are perfect but with your help we can be successful.
第（26）题选
连词辨析题。起初我只是生他们的气，但理查德让我思考他们为什么这样做。or或者，否则；but但是；for因为；and和。故本题选B。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
