In the following question, select the related letters from the given alternatives.
JRM : DLG :: TNL : ?

Each letter of the alphabet has corresponding number{ A-1, B-2, C-3,D-4,E-5 .......................... X-24,Y-25,Z-26}

JRM : DLG

Mapping J(10) to D(4) { difference between them is 6}

Mapping R(18) to L(12) { difference between them is 6}

Mapping M(13) to G(7) { difference between them is 6}

now following the same pattern as above we get

T (20) - 6 = 14 (N)

N(14) - 6 = 8 (H)

L (12) - 6 = 6(F)

hence 

TNL: NHF