单项选择题

A.当ν’≈0.5,则有Cv1≈Cv2≈Cv3
B.当ν’≈0.5,则有Cv1≈2Cv2≈3Cv3
C.当ν’=0,则有3Cv1=2Cv2=Cv3
D.当ν’=0,则有Cv1=Cv2=Cv3