根据材料内容，选择正确答案。

    Mr Smith had a week's holiday, so he said, "I'm going to see the sea by train." He put on his best clothes, took a small bag, went to the railway station and got onto the train. He wore a beautiful hat, and he often put his head out of the window during the trip and looked at the beautiful scenery. But suddenly the wind pulled his hat off.

    Mr Smith took his old bag and threw it out of the window quickly too. The others in the train laughed. "Is your bag going to bring back your beautiful hat?" they asked.

    "N0," Mr Smith answered, "but there is no name or address in my hat, and there's a name and an address on the bag. If someone finds both of them, he or she will send me the bag and the hat.''

材料一:公门有公，卿门有卿，贱有常辱，贵有常荣，赏不能劝其努力，罚亦不能戒其怠惰。

——《礼记》

材料二:汉代察举制“四科取士”为：“一曰德行高妙，志节清白；二曰学通行修，经中博士；三曰明达法令……四曰刚毅多略……皆有孝悌廉公之行”。

——《后汉书·百官志注》

材料三:九品访人，唯问中正。故据上品者，非公侯之子孙，则当涂之昆弟也。二者苟然，则荜门蓬户之俊，安得不有陆沈者哉！

——《晋书·段灼传》

材料四:唐人沈既济说：“故太平君子，唯门调户选，征文射策，以取禄位，此行己立身之美者也。父教其子，兄教其弟，无所易业，大者登台阁，小者任郡县，资身奉家，各得其足。是以五尺童子，耻不言文墨焉。是以进士为士林华选，四方观听，希其风采。每岁得第之人，不浃旬而周闻天下，故忠贤隽彦韫才毓行者，咸出于是。”

——转引自韩国磐《隋唐五代史论集》

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儿童一旦缺钙，容易患（    ）