According to the right-handed spiral law, the magnetic field generated by conductor A at point C is perpendicular to ac downward, and the magnetic field generated by conductor B at point C is perpendicular to bc downward. Because IA > IB, the magnetic field generated by conductor A at point C is stronger than that generated by conductor B at point C, so the resultant magnetic field is lower to the left. According to the left-handed rule, the direction of ampere force may be F4. So d is right, and A, B and C are wrong.

So choose D.