Explanation: A transformer's fundamental operation relies on the principle that the ratio of voltages across its windings is directly proportional to the ratio of the number of turns in those windings. Specifically, Vp/Vs = Np/Ns, where Vp and Vs are the primary and secondary voltages, and Np and Ns are the number of turns in the primary and secondary coils, respectively. For a transformer to "step up" its input voltage, the output voltage (Vs) must be higher than the input voltage (Vp). To achieve Vs > Vp, the number of turns on the secondary winding (Ns) must be greater than the number of turns on the primary winding (Np). Therefore, more turns on the secondary than on the primary are required. Conversely, option A (more turns on the primary) describes a step-down transformer, which reduces voltage. Option C (equal turns) describes an isolation or unity transformer, where the voltage remains the same (ignoring losses).