Which of these is included in material costs?

The correct answer identifies inspection of materials as part of material costs because it directly relates to ensuring the materials meet the necessary standards and specifications before they are used in construction. Inspection is a crucial step in the procurement of materials, as it helps to ascertain quality and compliance with building codes and regulations.

While labor charges, transportation costs, and contractor fees might be associated with the overall project expenses, they are classified differently. Labor charges relate to the workforce necessary to carry out the construction tasks. Transportation costs pertain to the expenses incurred to deliver materials to the job site, and contractor fees encompass the payment for the contractor's services in managing the project. All these costs are significant for the project's budget, but they do not fall under the category of material costs, which focus specifically on the purchasing and verification of the materials themselves.