“绿叶在光下制造有机物”实验步骤的正确顺序是（    ）

①用酒精去掉叶绿素                ②把天竺葵放在光下照射

③把天竺葵叶片用黑纸遮盖一部分      ④把天竺葵放在黑暗处一昼夜 

⑤把部分遮光的叶片摘下，去掉黑纸     ⑥用清水漂洗叶片后滴加碘酒．

已知函数f（x）=x²﹣x﹣2a

（1）若a=1，求函数f（x）的零点；

（2）若f（x）有零点，求a的范围．

    Julia's father, Mr Green is 40 years old. He has two brothers and three sisters. Julia's mother, Mrs. Green is a farmer. She has two brothers and two sisters. Julia has a brother, his name's Ben. Look! Ben is on the sofa. Julia is on the chair. Ben likes sports.He has basketballs and footballs.Julia doesn't like sports, she likes reading books.

判断两根钢条甲和乙是否有磁性时，可将它们分别靠近一枚小磁针。当钢条甲靠近时，小磁针自动远离；当钢条乙靠近时，小磁针自动接近，由此可知（   ）