Final answer:
A unit is considered an ICS single resource that represents an individual piece of equipment and its personnel complement within the Incident Command System.
Step-by-step explanation:
An ICS single resource refers to an individual piece of equipment and its personnel complement, or an established team that can be used within the Incident Command System (ICS). When looking at the options provided, 1) engine company, 2) unit, 3) strike team, and 4) company officer, the one that represents a single resource is a unit.
In ICS terminology, a unit typically refers to a vehicle with a specific designation and its personnel. An engine company may comprise multiple units, a company officer is an individual role within a company, and a strike team consists of multiple units of similar type and function but is a larger entity than a single resource. Therefore, the correct answer is unit.