Final answer:
The common factor of -12y^7x^2 - 9y^5 is -3y^5(4x^2y^2 + 3).
Step-by-step explanation:
To find the common factor of -12y^7x^2 - 9y^5, we can observe that both terms have a common factor of -3y^5. We can factor out this common factor to get:
-12y^7x^2 - 9y^5 = -3y^5(4x^2y^2 + 3)
So, the common factor is -3y^5, and the correct answer is option D) -3y^6(4x^2y^2 + 3).