For a wall made of several different slabs placed one after another, each having the same cross-sectional area, which statement is correct at steady state?
a) Heat current differs from slab to slab; the temperature drop is the same for all slabs.
b) Heat current is the same through every slab; the temperature drop across a slab is proportional to its thickness L only.
c) Heat current is the same through every slab; the temperature drop across a slab is proportional to kL of that slab.
d) Heat current is the same through every slab; the temperature drop across a slab is proportional to its thermal conductivity k.}