You have purchased a 'smart phone' which has a battery system advertised as allowing 22 hours of 'talk time' before it requires recharging. A friend of yours advises you that it is a good phone, but the 22 hours of 'talk time' is a highly theoretical number, based on ideal conditions concerning the placement of the phone towers around you as you talk, the exact number of calls you initiated while talking, and the state of the battery when you last charged the phone. As a result of these issues, your friend warns you that you can generally only expect 20 hours of 'talk time' from the battery system. Based on this discussion with your friend, the issue concerning the actual placement of the phone towers around you as you talk is best described by which of these concepts? a. the design capacity of the phone battery system b. a point of indifference in the phone battery system c. the effective capacity of the phone battery system d. a determinant of the effective capacity of the phone battery system e. the utilization of the phone battery system