*Question E2B12:
What signals SSTV receiving software to begin a new picture line?*  

*Correct Answer is  A: Specific tone frequencies*  

### AI Response: (may contain errors)  

In Slow Scan Television (SSTV), images are transmitted over radio waves by converting them into audio tones. The receiving software needs a way to know when to start a new line of the picture. This is done using specific tone frequencies.

### Explanation:

1. **Correct Answer: Specific tone frequencies**
   - SSTV uses specific tone frequencies to signal the start of a new line in the image. These frequencies act as a synchronization signal for the receiving software, ensuring that each line of the image is aligned correctly. For example, a common frequency used for this purpose is 1200 Hz, which indicates the start of a new line.

2. **Why the other choices are incorrect:**
   - **Elapsed time:** SSTV does not rely on elapsed time to start a new line because timing can vary due to transmission conditions. Using specific frequencies is more reliable for synchronization.
   - **Specific tone amplitudes:** Amplitude is not used for line synchronization in SSTV. Amplitude variations can occur due to signal fading and are not reliable for signaling.
   - **A two-tone signal:** While two-tone signals are used in some digital modes, SSTV specifically uses single tone frequencies for line synchronization, not a combination of two tones.

### Key Point:
- **Synchronization in SSTV:** Specific tone frequencies are crucial for ensuring that the receiving software correctly aligns each line of the image, maintaining the integrity of the transmitted picture.