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    The figure above shows the dimensions of a semicircular cross section of a one-way tunnel. The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel. If vehicles must clear the top of the tunnel by at least foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel?
    A. 5 ft
    B. 7 ft
    C. 8 ft
    D. 9 ft
    E. 10 ft
    題目翻譯：直徑為 20 ft 的半圓形交通隧道，行車道在隧道中央，寬 12 ft。要求過(guò)往車輛距隧道頂部最近處不能少于 1 ft，下列多高的車應(yīng)該被禁止通行?
    解答：題中已知這個(gè)半圓形的直徑是20ft，也就是說(shuō)半徑是10ft。已知行車道在路中間并且寬12ft，也就是在圓心兩側(cè)各占6ft。根據(jù)這兩個(gè)條件可以構(gòu)造出直角三角形并利用勾股定理進(jìn)行計(jì)算，得出限高7.2ft。選 CDE
    考點(diǎn)：對(duì)于幾何計(jì)算知識(shí)與勾股定理的考察。
    難點(diǎn)：對(duì)于題意的轉(zhuǎn)化。
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