导读：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 ftB. 7 ftC. 8 ftD. 9 ftE. 10
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
题目翻译：直径为 20 ft 的半圆形交通隧道，行车道在隧道中央，宽 12 ft。要求过往车辆距隧道顶部最近处不能少于 1 ft，下列多高的车应该被禁止通行?
解答：题中已知这个半圆形的直径是20ft，也就是说半径是10ft。已知行车道在路中间并且宽12ft，也就是在圆心两侧各占6ft。根据这两个条件可以构造出直角三角形并利用勾股定理进行计算，得出限高7.2ft。选 CDE
考点：对于几何计算知识与勾股定理的考察。
难点：对于题意的转化。
