Five statements about resistance and temperature are given. (i) The resistivity of copper rises almost uniformly with temperature near room temperature. (ii) The resistivity of nichrome changes only slightly over a wide range of temperature. (iii) A metal's resistivity rises on heating because it has fewer free electrons. (iv) A $10\ \Omega$ copper wire at $20\ ^\circ\text{C}$ becomes $13.2\ \Omega$ at $100\ ^\circ\text{C}$, for $\alpha = 4.0 \times 10^{-3}\ ^\circ\text{C}^{-1}$. (v) A semiconductor's resistivity falls on heating because its collisions become rarer. How many are correct?