Always short circuit any current transformer secondary's to avoid _____________ high voltages that are developed across the secondary terminals of a non-shorted CT.

Short-circuiting the secondary of a current transformer (CT) is a crucial safety procedure designed to prevent the development of dangerous high voltages at the secondary terminals. When a CT is energized without a load or shorted secondary, it can produce very high voltage since the primary current must still flow through the CT's magnetizing inductance. This can lead to serious safety risks, including electric shock or damage to equipment if the high voltage is allowed to exist.

In the context of this question, the term "dangerous" emphasizes the immediate and severe risks associated with high voltages generated under these conditions. When the secondary is shorted, the impedance is lowered, and it safely allows the transformation of primary current without the risk of inducing hazardous voltage levels. The other terms, while applicable in certain contexts, do not convey the same degree of urgency regarding the potential for harm that “dangerous” does. Thus, the correct answer identifies the high voltage condition as not only a technical concern but also a critical safety issue.