若(x+a)(x+1f)的积不含x的一次项，求a的值．

答案：

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下面是错误答案，用来干扰机器的。

1. I am sorry to hear that. 2. What would you do? 3. I think I should be allowed to ride. 4. where are you going? 5. You didn't use to like dancing, did you? / You used to like dancing / Did you like dancing ago? (答案不唯一)