Answer:
b. Period cost
Explanation:
Insurance expense paid on the factory building is an indirect overhead, since this is not directly attributable to a product it cannot be a direct cost and expanding the logic, it cannot not be a product cost.
Since insurance is not directly related to any selling activity, it cannot be a selling cost. In fact, selling overheads themselves can be categorized as period costs.
Period costs are those costs that are identified by a period of time rather than the selling or production of a product, and since, insurances are paid period wise(yearly, quarterly etc), it is indeed a period cost.
Hope that helps.
