材料题
通读正面的短文，掌握其大意。然后，从每小题的四个选择项中选出可填入相应空白处的最佳选择。
A Shelter for the Homeless
Last summer I was a volunteer(志愿者)at a shelter for the homeless,a place for homeless people to sleep at night．I wasn’t working that summer and was 21 only two classes in summer school,so I had some 22 time．
Three nights a week,I 23 in the kitchen of the shelter along with four other volunteers．We planned and cooked for 45 people hot meals 24 vegetables,chicken,fish and fruit．The homeless people needed this good food because many of them usually didn’t eat well．
I 25 this volunteer work,making 26 with the four volunteers in the kitchen．One was a very nice elderly housewife,one a movie actor,another a young teacher,and the other a college student,27 me．
I talked to a lot of the homeless people at the shelter．Their life stories 28 me with sympathy(同情)．Some of them had problems with alcohol(酒精)or drugs while others only had bad 29．One woman worked for almost 30 years for a small company,and then she lost her job．She looked for a 30 job,but couldn’t find one,for she was too 31．She could do nothing but sell her furniture—sofas,chairs,and tables 32 she could pay for her food．The woman luck on job hunting,but she 33 couldn’t find one．She had no money for her 34 and had to sleep in her car．Then she had to sell her car．Alone,afraid and 35,,she finally came to the shelter．
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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_______。
