单项选择题

低压加热器采用的堵头要求为()。

A.长约50mm,锥度为1:20,大端比管孔大0.025~0.05mm
B.长约40mm,锥度为1:25,大端比管孔大0.025~0.05mm
C.长约40mm,锥度为1:20,大端比管孔大0.025~0.05mm
D.长约50mm,锥度为1:25,大端比管孔大0.025~0.05mm