About reactivity in SN1reaction following statements are noted .Pick out the correct pair

Question

$\begin{array}{1 1}\text{ a)2-iodo 2-methyl butane reacts faster than t-butylchloride}\\ \text{ b)Ethyl iodide reacts faster than 2-bromo 2-methyl butane} \\ \text{ c)n-Propyl bromide reacts faster than 3-bromo cyclohexane } \\ \text{ d)Cyclohexyl bromide reacts faster than methyl iodide.}\end{array}$