单项选择题
图所示复合管,已知T1的β1 = 30,T2的β2 = 50,则复合管的β约为()
A.1500
B.80
C.50
D.30
图所示复合管,已知T1的β1 = 30,T2的β2 = 50,则复合管的β约为()
A.1500
B.80
C.50
D.30