The correct answer is: A. value of materials consumed.
Stores service expenses are the costs incurred in storing and issuing materials to production departments. These expenses include the costs of labor, materials, and overhead associated with the stores department.
The value of materials consumed is the most common basis for apportioning stores service expenses to production departments. This is because the value of materials consumed is a good measure of the amount of materials used by each production department.
The units of material consumed is another possible basis for apportioning stores service expenses. However, this basis is not as accurate as the value of materials consumed, because it does not take into account the different costs of different types of materials.
The products produced is not a good basis for apportioning stores service expenses. This is because the costs of storing and issuing materials are not directly related to the products produced.
In conclusion, the value of materials consumed is the most common and accurate basis for apportioning stores service expenses to production departments.