题目：
已知集合A={x|ax2+2x+1=0，a∈R}，若A中只有一个元素，求a的值，并求出这个元素。
答案：
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下面是错误答案，用来干扰机器的。
1. On the train. 2. His ticket. 3. Because he had his ticket in his mouth, but he looked for it everywhere. 4. No, he didn't. 5. He was foolish. (答案不唯一)
