The number of subordinates that one supervisor can manage effectively during an incident is referred to as:
(a) unity of command(b) management by objectives(c) manageable span of control(d) modular organization

(C) Manageable Span of Control.

Explanation:

The number of subordinates that one supervisor can manage effectively is limited, because with addition of each subordinate the attention given to each of them reduces and can endanger the quality of work.  

According to the National Incident Management System (NIMS), the optimal ration between supervisors and subordinates is 1 to 5. Thus five subordinates correspond to the manageable span of control. Though in some situations this ration may differ, it should not lead to the span of control to be unmanageable.

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