The answer is 'D'
When you divide 48 and 78 by 2, you get 24 and 39. Then divide 24 and 39 by 3 and you will get 8 and 13, which don't have any common factors.
The same happens with 12 and 30...
When 12 and 30 are divided by 2, you get 6 and 15. Then divide 6 and 15 by 3 and you get 2 and 5, which have no more common factors.