题干

空气质量是人们日益关注的一个话题,越来越多的人经常查询PM2.5实时数据来了解空气质量情况.PM2.5是指大气中直径小于或等于2.5μm的颗粒物,2.5μm相当于____m.PM2.5在空气中含量浓度越高,就表示空气污染越严重.为了控制和消除大气污染,很重要的一个方面是要发展新的理想能源.太阳能作为未来的理想能源,它属于 ____

(填“可再生”或“不可再生”)能源.在太阳内部,氢原子核在超高温下发生  ____

(填“聚变”或“裂变”),释放出巨大的核能.

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2.5×10-6,可再生,聚变

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    Recently, I experienced a wonderful lesson in how little things still mean a lot. My brother, mother and I live in a very rural district of Hawaii. Our farm is at least a dozen miles from the most basic of services. Therefore, I take weekly trips to COSTCO to get supplies. About a month ago, I finished loading up the car and was about to leave, when a piece of paper caught my eye. I picked it up and read it carefully.

    It was a receipt(收据) from the State Motor Vehicle Division, recording the owner's payment of her Vehicle's Registration fees. At first I thought that I could find the owner. So I waited there for about an hour. Although the receipt had been borne (由……携带) on the wind, where in the busy, crowded parking lot would I find the owner? I looked over the receipt for contact or any personal data, perhaps a license tag(牌照)or telephone number. I checked the date, the fees paid, noted the name of the owner and pocketed the paper. I concluded that the best and easiest step to take was to put the receipt in an envelope and send it to the owner first the next morning.

    By the end of the week, I received a beautiful thank-you letter from a very grateful and happy woman containing a handwritten message and a gift card. In the letter, the woman explained how the wind snatched(夺去) her receipt from a pocket in her car's passenger door. She had searched everywhere for quite some time before giving up.

    It felt great to know I'd helped someone avoid a loss by doing something that at first glance(一瞥) seemed little or even unimportant.