有一串彩灯是按2红、3绿、5黄的顺序依次排列的．第21盏彩灯是______色，前80盏中，有______盏绿灯．
这串彩灯按照颜色特点排列的规律是：10盏灯一个循环周期，分别按照：2红、3绿、5黄的顺序依次循环排列，
21÷10=2…1，所以第21盏彩灯是第3周期的第1个，是红灯；
80÷10=8，即前80盏灯经历了8个周期，
8×3=24（盏）；
答：第21盏彩灯是红色，前80盏中，有24盏绿灯．
故答案为：红；24．
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| 2. A: I want to buy a present for my sister. B: ? A: Good idea! | Why don't you. . . ?  |
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