The thermal conductivity of a solid depends upon the solid’s temperature as k = a T+b where a and b are constants. The temperature in a planar layer of this solid as it conducts heat is given by:a. aT+b= x +C2b. aT+ b = C1x^2 +C2c. aT^2+ bT= C1x+ C2d. aT^2+ +bT= C1x^2+ C2e. None of these