In the following question, select the related letters from the given alternatives. NK : JG :: SF : ?

OB UA BU AS

OB

Logic here is : NK : JG N(14) - 4 = (10)J , K(11) - 4 = (7)G Similarly , SF : ? S(19) - 4 = (15)O ,F(6) - 4 = (2)B OB is correct answer .