Maintenance costs can include which of the following?

Maintenance costs primarily revolve around the expenses associated with keeping equipment, facilities, and systems in good working condition. This includes both proactive maintenance, which aims to prevent breakdowns through regular inspections and servicing, and reactive maintenance, which involves repairs after a failure has occurred. This dual aspect of proactive and reactive maintenance aligns perfectly with the definition of maintenance costs, making this the correct choice.

Utility bills for operational facilities are generally categorized under overhead costs rather than maintenance specifically. Staff salaries for administrative roles often fall under administrative or operational expenses, which do not directly relate to maintenance. Lastly, marketing and client engagement expenses are considered business development costs and are unrelated to maintaining physical assets or systems. Therefore, the correct option encapsulates the core idea of maintenance costs accurately.