我国新修订的《环境空气质量标准》中增加了PM2.5检测指标，“PM2.5”是指大气中危害健康的直径小于或等于2.5微米的颗粒物，2.5微米即0.0000025米．用科学记数法表示0.0000025为（   ）

       Last week our class went to the zoo as part of our science project. We spent a few hours1there. We didn't do much studying. We just had a good 2 . We left for the zoo by bus at 9:00 and 3 at the zoo half an hour later. There are all kinds of 4 in the zoo. And the animals have many good 5 for us. We all wanted to watch the elephant show at 10:00. But before that we went to look at snakes because it was a part of our project. I don't like snakes because they are so 6. The elephant show lasted 45 minutes. It was really nice. I didn't know elephants can play soccer so 7! Then we had a 15-minute break for a drink, we went 8  the zoo trying to see as many animals as we could before 9. Lunch was fun because we had it 10 monkeys. We went back on the bus at 2:00. It took 30 minutes to get back to school.