In this scenario, we have three resistors of equal value \( R \) connected in a triangular arrangement. We know the voltage across AB is \( 12V \).
The total resistance between A and B, and A and C can be found by recognizing that in a triangle, the total resistance between two points is given by the sum of the resistances in the paths through the network.
The current splits evenly between the two paths (since all resistors are identical). Therefore, the ratio of the current through AB to ACB is \( 1:1 \).
Thus, the correct answer is \( 1:1 \).