Which of the following assumptions has been used to obtain the relation $\frac{\text{v}_\text{s}}{\text{v}_\text{p}} = \frac{\text{N}_\text{s}}{\text{N}_\text{p}}$ for a transformer ? (A) The resistance of the primary coil is large. (B) The same flux links both the primary and the secondary coils. (C) The resistance of secondary coil is large. (D) The transformer is $100%$ efficient.