Metalled and unmetalled varieties are types.

Explanation:
 Metalled and unmetalled varieties are seen in the types of the road which is used for any means of transport. So they are types of roads.
Metalled roads consist of successive layers of smaller stones until the road surface was composed of small stones, which results in a compact and hard surface. These are generally made up of cement concrete or coal tar.
Unmetalled roads are generally seen in the rural areas, which consist of mud and gravel.

Final Answer:
Hence, the correct answer is option B. i.e, Roads