Direct expenses are those which can be identified with particular products. Which of the following items is a direct cost?

c.
A royalty paid to the holder of a patent after each item is produced.
 

Rent of the factory will be Factory overhead therefore not a irect cost royalities paid are also not attributable to unit products there for i think answer can be from B or D  

Rent is indirect because it does not directly attribute to the product.
The rest are direct costs because without it the product shall not be completed.

a.
The rent of the factory in which products are made.

In this case we can distinct betwwen direct / indirect costs as follows :-  Direct costs are :-  c.
  royalty paid to the holder of a patent after each item is produced.
Indirect costs are :-  a.
The rent of the factory in which products are made.
b.
The wages of the production supervisor.
d.
The cost of the glue used to attach labels to the products.

Option d   The cost of the glue used to attach labels to the products.