求翻译GRE数学题
Thefigureaboveshowsthedimensionsofasemicircularcrosssectionofaone-waytunnel.Thesingletrafficlaneis12feetwideandisequidistantfromthesidesofthetunnel.Ifvehiclesmustclearthetopofthetunnelbyatleastfootwhentheyareinsidethetrafficlane,whatshouldbethelimitontheheightofvehiclesthatareallowedtousethetunnel?
A.5ft
B.7ft
C.8ft
D.9ft
E.10ft
图就是一个半圆,上面标出直径为20ft
我现在看不懂题目.不知道说什么意思.求教高人
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