Temperature dependence of resistivity ρ(T)

Question:
Temperature dependence of resistivity ρ(T) of semiconductors, insulators, and metals is significantly based on the following factors:

(a) number of charge carriers can change with temperature T

(b) time interval between two successive collisions can depend on T

(c) length of material can be a function of T

(d) mass of carriers is a function of T

Solution:

The correct answer is