C15: The figure shows a composite slab of three different materials with equal thicknesses but different thermal conduction. The opposite sides of the composite slabs are held at fixed temperatures T₁ and T₂.

Given that k_B > k_A > k_C, list the materials in order of the temperature difference across them, starting with the smallest.

A B C

T₁ T₂

1) A-B-C

2) B-C-A

3) C-A-B

4) B-A-C

5) A-C-B