Classify each of the following costs as manufacturing or nonmanufacturing:

a. direct labor

b. sales commissions

c. depreciation on delivery trucks

d. salary and bonus for the chief executive officer

e. direct materials

f. product design staff salaries g. advertising h. property taxes on the corporate headquarters building i. gas and electricity for the factory j. accounting-office staff salaries k. operators of product help lines for customers l. customer credit evaluation staff salaries