Which statement about SIA and CID is correct?

• A. SIA uses rotary or pulse dialing; CID uses tone dialing.
• B. SIA uses tone dialing; CID uses pulse dialing.
• C. CID is faster and less distortion-prone than SIA.
• D. Both formats rely on pulse dialing.

Answer: (A)

Digits are sent over a telephone line in two classic ways: as pulses or as tones. SIA signaling uses pulse dialing, the old rotary-dial way where each digit is represented by a series of on/off pulses. CID signaling uses tone dialing, specifically DTMF tones, where each digit is encoded as a pair of tones. That difference—pulse for SIA versus tone for CID—is why that statement is correct. In practice, tone signaling is faster and generally more robust on modern lines, but the key point the item tests is which method each format uses. The other options mix up which format uses pulse or tone or claim a speed advantage that doesn’t define the formats themselves.