单项选择题

若焊缝长度大于等于500mm,焊缝两端__mm范围内禁止定位焊;若焊缝长度小于500mm,焊缝两端的__mm范围内禁止定位焊()

A.20mm,50mm
B.50mm,20mm
C.10mm,20mm
D.20mm,10mm