Which one of the following statements expresses a true proportion?
A3 : 5 = 12 : 20
B42 : 7 = 6 : 2
C2 : 3 = 3 : 2
D14 : 6 = 28 : 18
A3 : 5 = 12 : 20
B42 : 7 = 6 : 2
C2 : 3 = 3 : 2
D14 : 6 = 28 : 18