2010年上海世博会中国馆――“东方之冠”给人强烈的视觉冲击，它的主体结构为四根巨型钢筋混凝土制成的核心筒。其中钢属于(   )

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       Both the British and Americans speak English. However, there are several differences between American English and British English. For example, the words they use in daily life are not the same. The British call the first floor of a building the ground floor. The floor above the ground floor is the first floor, which Americans call the second floor. Once you go to Britain and America, you may notice other differences. The British usually hide their feelings. They don't often start a talk with strangers. On the train the British often spend their time reading newspapers or books. But Americans are more active and easier to talk with.

三角形的面积为12cm²，把它的底y表示成这边上的高x的函数，那么表达式是　____ 　，其图象位于第____ 象限．