Answer: C. 1, 2, 4
Explanation:
 A factor is an integer that is a divisor of a number. In other words, the number can be divided by this integer and result in another integer.
 To answer this question, we can list the factors of both numbers. I have underlined and bolded integers that appear in both lists, giving us our answer.
 Factors of 16: 1, 2, 4, 8 and 16
 Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36
 C. 1, 2, 4