I worked for a short time as a cashier at a restaurant a few months ago. I also helped to clean up the tables when it was very busy. One night, just before Christmas, I found a large black wallet on the floor near one of the tables. I guessed I should check it to find out who was the owner, but I was very busy at the time. And I imagined that if there was something valuable in the wallet, the owner would be back. Sure enough, an hour later a man came up to the counter and asked if anyone had found a wallet. l asked him to describe the lost wallet, and after he described it exactly, I gave him the wallet. He expressed his thanks when I handed it to him. He asked me if I had opened it, and when I told him “no”. At once he opened it and showed that it had nearly $800 in cash. He took out a twenty-dollar bill and handed it to me and I was amazed at this. “A reward for your honesty,” he said and then turned and walked away.
Thinking about it later, I began wondering whether I would have been honest if had known what was in the wallet! I thought that if I had no way to find the owner and no one returned to get it, I might keep it. But it also came into my mind that I actually saved someone's Christmas plans by finding and returning the wallet. The good feeling it gave me was worth more than anything could buy.
The writer returned the wallet to the owner because____.（ ）
根据文章最后一段中的“Thinking about it later, I began wondering whether…”可排除选项C和D。比较选项A和B，再结合文章大意，选B为佳。
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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
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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_______。
