A.20米 B.30米 C.40米 D.50米
A.≦b/1000且<10mm,b:塔腳跨距 B.≦b/1500且<10mm,b:塔腳跨距 C.≦b/1000且<15mm,b:塔腳跨距 D.≦b/1500且<15mm,b:塔腳跨距
A.400mm B.500mm C.600mm D.700mm