Into which of the three elements of manufacturing cost would each of the following e classified?

a. Tubing used in manufacturing bicycles.

b. Wages paid by an automobile manufacturer to employees who test-drive completed automobiles.

c. Property taxes on a manufacturing facility.

d. Gold bullion use by a jewerly manufacturer.

e. Wages of assembly-line workers who package frozen food.

f. Salary of plant superintendent.

g. Electricity used in factory operations.

h. Salary of a nurse in a factory first-aid station.