Answer: A. 2
Solution:
The greatest common factor of two or more numbers is the highest factor that can be used in dividing all the numbers.
E1 = 4k = 2×2×k
E2 = 18k4 = 2 × 3 × 3 × k × k × k × k
E3 = 12 = 2×2×3
The number or expression they all have in common is 2.
This makes 2 the greatest common factor.