Indicate whether each of the following costs of an airplane manufacturer would be classified as direct materials

Question:

Indicate whether each of the following costs of an airplane manufacturer would be classified as direct materials cost, direct labor cost, or factory overhead cost:
a. Controls for flight deck
b. Aircraft engines
c. Depreciation of welding equipment
d. Welding machinery lubricants
e. Salary of test pilot
f. Steel used in landing gear
g. Wages of assembly line worker
h. Tires