1. False. Continuous integration is about integrating the work of every developer with that of their colleagues at least daily and building and testing the integrated sources. Just running a daily build does not constitute continuous integration.
2. True. A classic build pipeline is always connected to a source code repository. It might be that the sources are not used in the build pipeline, but the connection is always there.
3. False. It is possible to create a YAML pipeline that starts directly with a stage. A link to a source control repository is no longer mandatory.
4. The correct answer is number 1: a service connection. Service connections are configured in the organization or project that contains the pipeline that needs to call into the external tool. Once a service connection is configured, it can be used from one or more pipelines.
5. The correct answers are numbers 1 and 3: access to closed networks and the ability to install extra software. Self-hosted agents are deployed on infrastructure owned by you. This means that you can deploy them on networks that you control, giving them network access to that network. Since the agents are deployed on your infrastructure, you can also decide on which software is installed (and which is not). Tasks and extension tasks are automatically downloaded to the agent before it executes a job. You can have as many parallel pipelines as you want without using self-hosted agents. However, you will need to buy extra parallel executions from Microsoft for this purpose.