Explanation: TTL (Transistor-Transistor Logic) integrated circuits are a foundational family of digital logic widely used in electronics, including many amateur radio projects and equipment. These devices are specifically designed to operate with a nominal power supply voltage of **5 volts DC**. This voltage provides the correct bias for the internal transistors and ensures reliable switching between logic "high" and logic "low" states. * **A) 12 volts** and **B) 13.6 volts** are common power supply voltages for general amateur radio equipment, often derived from car batteries or AC-to-DC converters. However, these voltages are significantly too high for standard TTL ICs and would likely cause irreparable damage. * **C) 1 volt** is far too low to properly power TTL circuits, which require a higher voltage to define their logic levels and operate their internal components.