A) GHS
the first sequence is ABP --> CDQ --> EFR --> the next could be clearly starting with GH
as first sequence is starting with AB
2nd sequence is starting with CD
3rd sequence is starting with EF
So, the next sequence could be starting with GH.
Now, in the first sequence after AB is P
in the 2nd one after CD is Q
in the 3rd one after EF is R
So, the 4th one must be GH S.