Identify the following costs as direct materials (DM), direct labor (DL), or factory overhead (FO) for a

Question:

Identify the following costs as direct materials (DM), direct labor (DL), or factory overhead (FO) for a textbook publisher.
a. Maintenance on printing machines
b. Glue used to bind books
c. Wages of printing machine employees
d. Paper used to make a textbook