Consider the following statements.
(A) When temperature difference across the two sides of a wall is increased, its thermal conductivity increases.
(B) Thermal conductivity depends upon the temperature difference across the two sides of a wall.

Select the correct option.
(a) (A) is false but (B) is true.
(b) Both (A) and (B) are true.
(c) (A) is true but (B) is false.
(d) Both (A) and (B) are false.