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From: terri  wombat. Com. Au To: (happylizijun)  yaboo. com. cn Subject: My school Hi, Li Zijun, Thanks very much for your email. I really enjoyed reading it. I think we have a lot in common. I wonder if our school life is similar too. I go to a big high school in Sydney called Maylands High School. There are about 1000 students and 80 or so teachers. My class has 25 students in it, which is normal for a Year 11 class. In the junior school there are about 30 students in a class. In the senior high school we have lots of subjects to choose from, like maths, physics, chemistry, biology白色粉末A，由Na2SO4、Na2CO3、BaCl2、NaCl中的三种物质混合而成．把A加入到适量水中后，可得到白色沉淀B和溶液C，则：（1）若B能全部溶于稀硝酸时，A的成分为    ；（2）若B只能部分溶于稀硝酸时，A的成分为    ；（3）若B不能溶于稀硝酸时，A的成分为    ；（4）溶液C中一定存在的溶质是    ．