Refer to the exhibits.
This Mule application has an HTTP Request that is configured with hardcoded values. To change this, the Mule application is configured to use a properties file named config.yaml.
What valid expression can the HTTP Request host value be set to so that it is no longer hardcoded?
To refer to variables from a properties file in Mule applications, the correct syntax utilizes `${variableName}`. Therefore, to reference the 'host' value from the 'training' configuration in the config.yaml file, the valid expression is `${training.host}`.
a dot, dollar sign and curly braces.
C. ${training.host}