The correct answer is B) effective value. The root mean square (RMS) value of a sine-wave current is equal to the effective value of the current. The effective value represents the amount of direct current (DC) that would produce the same amount of power as the alternating current (AC) in a given load. This is important because the effective value is the value that is typically used to measure and report AC electrical quantities, as it provides a meaningful representation of the power being delivered. The other options are incorrect because the instantaneous value (A) refers to the value of the current at a specific point in time, the maximum value (C) is the peak value of the sine wave, and the average value (D) is the average of the sine wave over a full cycle, which is zero for a pure sine wave.