The Diagram Shows Four Slabs of Different Materials with Equal

The diagram shows four slabs of different materials with equal thickness, placed side by side. Heat flows from left to right and the steady-state temperatures of the interfaces are given. Rank the materials according to their rates of thermal conduction, smallest to largest.

A) 1, 2, 3, 4
B) 2, 1, 3, 4
C) 1, 2, 4, 3
D) 3, 4, 2, 1
E) all are equal