Instructions: Answer the following questions in two to three sentences, drawing all information directly from the provided source context.

1. What is the primary recommendation of document ITU-R BO.1130-4?
2. List the five Digital Systems evaluated in the document and the general types of receivers for which they are intended.
3. Describe the key features of Digital System A’s design for handling multipath and shadowing environments.
4. How does Digital System B mitigate the effects of signal blockage, a common problem in satellite broadcasting?
5. What is the main purpose of Digital System D_S, and what audio coding algorithm is it based on?
6. Explain the core concept of the hybrid satellite/terrestrial system as implemented in Digital System D_H.
7. What are “gap-fillers” in the context of Digital System E, and what is their function?
8. Digital System A has three distinct transmission modes. What are they, and for what applications is each mode best suited?
9. According to the provided tables, how do the data rate ranges and audio codecs of Digital System A and Digital System B compare?
10. What is Multi-carrier modulation (MCM), and which system uses it to extend its capabilities for terrestrial delivery?