The correct option is A 12
The factors of 36 are : 1, 2, 3, 4, 6, 9, 12, 18 and 36.
The factors of 48 are : 1, 2, 3, 4, 6, 8, 12, 16, 24 and 48.
From the above, the common factors are 1, 2, 3, 4, 6 and 12.
So, the greatest factor among the common factors is 12.