Why do we wear woollen clothes in winter?

Question

$\begin{array}{1 1} (a)\; \text{to maintain the cold temperature} \\ (b)\; \text{to allow free flow of air} \\ (c)\; \text{to keep ourselves warm. } \\ (d)\; \text{keep us safe from heat, cold, rain, wind, and insect bites. } \end{array}$