Correct answer is ${training.host}
-------------------------------------------------------------------------------------------------------------------------------------------------- How to Configure Properties to Mule 4.X Platform?
1) Go to /src/main/resources project directory.
2) Create a configuration file with the name configuration.yaml inside the newly created config folder.

3) Go To Project > Global Element > Create > General >select the configuration.yaml file create in step- 2)

4) To verify develop a simple flow with HTTP listener which has above entries. Put the logger that prints the values on console.

5) Additional info: Similarly, when you want to access this port in DataWeave you need to use p function

Pick First is not valid type. Rest all are valid type of event processor.
Choice : https://docs.mulesoft.com/mule-runtime/4.3/choice-router-concept Round Robin : https://docs.mulesoft.com/mule-runtime/4.3/round-robin First Successful : https://docs.mulesoft.com/mule-runtime/4.3/first-successful

Error in validation component will get processed by Processer level On Error Propagate block and then error will be rethrown which will get processed by flow level error handler which will set payload to "Error- main flow". Hence correct answer is Error - main flow
1) Request is received by HTTP listener
2) Try scope gets executed
3) The validator component in the Try scope creates an Error Object because the payload is not null.
4) The On Error Propagate handles the error. The payload is set to "Error - Try scope"
6) "Error - Try scope" is returned to the 'On Error Continue' block. Main flow execution stops. Payload is set to "Error - main flow"
7) "Error - main flow" is returned to the requestor in the body of the HTTP request. HTTP Status Code: 200
------------------------------------------------------------------------------------------------------------------------------------------ Reference Diagram though not exactly same, conditions are similar. They will help you answer any new question on error handling in real exam:

https://docs.mulesoft.com/mule-runtime/4.3/on-error-scope-concept#on-error-continue