In data communications, ________ transmission uses a single conductor (plus a reference/ground) to send bits one after another over time.

Introduction / Context:
Communication links move data as electrical signals. Two fundamental strategies exist: serial and parallel. Knowing which one uses a single data path is essential for understanding interfaces like UART, SPI, and USB.

Given Data / Assumptions:

• A single conductor plus a reference (ground) is typical for one data line.
• Bits can be transmitted sequentially (serial) or simultaneously on multiple lines (parallel).
• We are identifying the transmission mode that fits “one conductor” carrying data bits over time.

Concept / Approach:
Serial transmission sends bits sequentially over one data line, often with a clock or embedded timing. Parallel transmission uses multiple conductors (one per bit or group of bits). The phrase “single conductor is used” aligns with serial data transport.

Step-by-Step Solution:

Verification / Alternative check:
Standards such as RS-232 (with a dedicated TX line) and single-wire protocols exemplify serial transmission over minimal conductors.

Why Other Options Are Wrong:
digital: describes the nature of signals, not the number of conductors.

automatic: not a transmission topology.

binary: describes symbol set (0/1) rather than wiring method.

Common Pitfalls:
Assuming serial always means one total wire; practical links may use additional lines for ground, clock, or control, but only one primary data conductor is needed for serial data flow.

Final Answer:
serial