A.1~2mm B.2~3mm C.1~3mm D.3~5mm
A.2/1000-3/1000 B.3/100-5/100 C.1/1000-3/1000 D.1/100-3/100
A.長(zhǎng)向跨度≧3m B.短向跨度≧3m C.長(zhǎng)向跨度≧4m D.短向跨度≧4m