The factors of 117 are: 1, 3, 9, 13, 39, and 117
The factors of 99 are: 1, 3, 9, 11, 33, and 99
The factors of 126 are: 1, 2, 3, 6, 7, 9, 14, 18, 21, 42, 63, and 126
The greatest common factors of 117, 99, and 126 are: 1, 3, and 9. And according to your answer choices your answer is C. 9