题干

一个空瓶子的质量是150g,当装满水时,瓶和水的总质量是400g;当装满另一种液体时,瓶和液体的总质量是350g.则这个瓶子的容积是____ cm3,另一种液体的密度是____ kg/m3.如果一定质量的空气受热体积膨胀,其密度变____.
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250,0.8×103,小

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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.