Four number-pairs have been given, out of which three are alike in some manner and one is different. Select the number-pair that is different from the rest.

18 : 49

THE LOGIC FOLLOWED HERE IS;

1) 23 : 52,

23+52 = 75(NOT PRIME NUMBER)

2) 18 : 49,

18+49 = 67(PRIME NUMBER)

3) 7 : 37,

7+37 = 44(NOT PRIME NUMBER)

4) 13 : 29,

13+29 = 42(NOT PRIME NUMBER)

Thus, 18 : 49 is the odd one.