單項選擇題
A.2mm B.4mm C.6mm D.8mm
A.小于箍筋直徑的3倍 B.小于箍筋直徑的5倍 C.小于箍筋直徑的8倍 D.小于箍筋直徑的10倍
A.5~10mm B.10~15mm C.15~20mm D.20~25mm