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    Hi, I'm Mo Hongwei from Changsha, Hunan. I'm going to enjoy myself during the New Year holiday. On 1st January, I'm going to stay at home and do my homework. On the morning of 2nd January, I'm going to meet my grandfather's friend Mr. Smith at the train station. In the afternoon, I'm going to take Mr. Smith around my school. In the evening, we're going to have a welcome party for him. On the morning of 3rd January, I'm going to ask Mr. Smith to teach me to write with the left hand. And I'm going to ask him to give me some advice(建议) about reading. I think my New Year holiday is going to be fun.

一元二次方程x²﹣4=0的根为（　　）