题目

磷酸镁铵(NH4MgPO4)是一种重要的盐，难溶于水。化学上制备磷酸镁铵从反应原理看，是用氯化镁、磷酸氢二钠和氨水混合反应的方法。(1)写出制备磷酸镁铵反应的离子方程式：__________________________________。(2)在实际制备的反应中，要向混合液中加入适量的铵盐(NH)，则加入铵盐的目的是__________________________________。“Everything happens for the best,” my mother said whenever things weren’t going my way. “Don’t worry, one day your luck will change.” Mother was right, as I discovered after I had finished my college education. I had decided to try for a job in radio. One day, I wanted to host(主持) a sports program. I went to Chicago and knocked on the door of every station. But I got turned down every time. In one station, a kind lady said my problem was that I hadn’t got enough experience. “ Get some work with a small station and work your way up,” she said. I went back home. I couldn’t get a job there, either. Then my dad told me a businessman had opened a store and needed someone to help him. But again, I didn’t get the job. I felt really down. “ Your luck will change,” Mom said to me. Dad lent me the car to help me to look for my job. I tried another radio station in Iowa. But the owner, a nice man, told me he had already had someone. As I left his office, I asked, “How can someone be a sports announcer(播音员) if he can’t get a job in a radio station?” I was waiting for the lift when I heard the man call. “ What did you mean? Do you know anything about football?” He put me in front of a microphone and asked me to try to imagine that I was giving my opinion on a football game, I succeeded. On my way home, Mom’s words came back to me, “One day your luck will change, Son. And when it happens, it’ll feel doubly(加倍的) good because of all the hard work you’ve had.” At that moment I knew what just what she meant. 46. What’s the writer’s ideal(理想的) job? A. A  sportsman   B. A  shop assistant    C. A  sports announcer   D. A  businessman 47. Why didn’t the writer get the job in Chicago?  A. because he was too young        B. Because he didn’t get college education C. Because he’s got a good-looking person D. Because he hadn’t got enough experience 48. Which of the following is true according to the article? A. You just need wait for some time, then luck will come. B. Luck will come if you try your best to do everything. C. It’s important for you to wait for luck. D. You should trust your mother. 49. The sentence “But I got turned down every time.” Means “______” A. But I was refused every time  B. But I was successful every time C. But I lost my way every time D. But the door of every station was always closed 50. What’s the best title of this passage? A. Mother’s words            B. Everything Happens For The Best  C. No One Is Always Lucky     D. To Find A Job In Radio Is Difficult