The greatest common factor (GCF) of 12 and 16 can be found by identifying the factors of each number.
The factors of 12 are: 1, 2, 3, 4, 6, 12
The factors of 16 are: 1, 2, 4, 8, 16
The common factors are: 1, 2, 4
The greatest of these common factors is 4.
Therefore, the answer is:
A. 4