把a、b、c、d四块金属片浸入稀酸中，用导线两两相连组成原电池．若a、b相连时，a为负极；c、d相连时，电流由d到c；a、c相连时，c极上产生大量气泡；b、d相连时，b极上有大量气泡产生．则四种金属的活动性顺序由强到弱为（ ）
A．a＞b＞c＞d
B．c＞a＞b＞d
C．a＞c＞d＞b
D．b＞d＞c＞a
形成原电池时，活泼金属做负极，若a、b相连时，a为负极，则金属活动性a＞b，c、d相连时，电流由d到c，则c为负极，活动性c＞d，a、c相连时，c极上产生大量气泡，说明在c极上产生氢气，c极上发生还原反应，c极为正极，则活动性a＞c，b、d相连时，b极上有大量气泡产生，说明在b极上产生氢气，b极上发生还原反应，b极为正极，则活动性d＞b，所以四种金属的活动性顺序为a＞c＞d＞b，
故选C．
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| That summer, my parents shook my entire world and turned it upside down when they told me they were getting a divorce (离婚). I couldn't 1 that our family was going to break up. Though I always knew my parents weren't very happy and they often 2 with each other, I 3 wanted my family to stay the same. My life changed 4 after my parents' divorce. My mother and I moved into a small apartment across town 5 my father and brother, Bill, stayed in our house. I now became a(n) 6 whenever I went to see my dad and Bill on the weekends. And immediately I had my soon-to-be stepfather, Dan, 7 I showed no interest. I was clearly 8 , especially after Dan and my mother married and I realized that there was 9 that things could change back to the way they were. Even though I 10 all Dan's attempts to get to know me and wasn't very nice to him, he never gave up on me. Gradually, I began to 11 him. I realized that we actually had some things 12 , especially when it 13 films and TV shows. We spent a lot more time together watching TV. That gave us a chance to communicate with each other. 14 still, Dan showed much more interest in me than my own father. Dan was always around when I needed advice 15 school or making friends. I began to warm up to Dan. The three of us 16 go out to eat and take short trips. 17 , I discovered that I had the happy family again that I had always wanted. I now realize it was 18 of my parents to get the divorce. Their breakup was the 19 thing to us all. My father also found happiness- he remarried and had 20 child, my half-sister, Michelle. That year when I was 13, I learned an important truth-change is not always the worst thing that can happen. Sometimes, it is just what we need the most. | ||||
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