In a certain code language, 'That was his sister' is coded as 'Bo Uv Zs Mn', 'This was his cat' is coded as 'Zs Pt Uv Ga' and 'That was my father' is coded as 'Bo Uv Ex Yz'. What is the code for 'sister' in this code language?

Mn

The pattern here;

THAT  WAS  HIS  SISTER  =  BO  UV  ZS  MN

THIS  WAS  HIS  CAT  =  ZS  PT  UV  GA

THAT  WAS  MY FATHER  =  BO  UV  EX  YZ

Thus, SISITER is coded as MN.