1. The problem asks us to find the common factors of 12 and 20. 2. Factors of a number are integers that divide the number exactly without leaving a remainder. 3. Given factors: - Factors of 12: $1, 2, 3, 4, 6, 12$ - Factors of 20: $1, 2, 4, 5, 10, 20$ 4. To find common factors, we look for numbers that appear in both lists. 5. Comparing the two lists, the common factors are $1, 2, 4$. 6. Therefore, the numbers from the choices $1, 2, 3, 4, 5, 6, 10, 12, 20$ that are common factors of 12 and 20 are: $$1, 2, 4$$ Final answer: $1, 2, 4$