请教！这道题是什么意思？

dearsue

The figureabove shows the dimensions of a semicircular cross section of a one-waytunnel.  The single traffic lane is 12feet wide and is equidistant from the sides of the tunnel.  If vehicles must clear the top of the tunnelby at least ½ foot when they are inside the traffic lane, what should be thelimit on the height of vehicles that are allowed to use the tunnel?
A.    5½ ft

B.     7½ ft

C.     8 ½ ft

D.    9½ ft

E.     10 ft

zliycdr

虽然题目么看懂，不过感觉20/2-1/2~

allennuli

LZ想象一下一辆12feet宽的汽车要通过隧道所能取的最大高度，再把这个高度减去1/2foot就行了

a10285

同意ls，半圆形隧道直径20，则铁轨12且与两边距离相等（4），要求vehicle至少与隧道顶部距1/2
如vehicle与隧道顶部接触，根据勾股定理，根号(10^2-6^2)=8，8-1/2= 7½ ft     选B.