Correct answer is process layer as all the orchestration and transformation logic should be in process layer as per Mulesoft's recommended approach for API led connectivity.
API-led connectivity is a methodical way to connect data to applications through reusableand purposeful APIs. These APIs are developed to play a specific role - unlocking data from systems, composing data into processes, or delivering an experience.
What are the APIs that enable API-led connectivity?
API-led connectivity provides an approach for connecting and exposing assets. With this approach, rather than connecting things point-to-point, every asset becomes a managed API - a modern API, which makes it discoverable through self-service without losing control.
The APIs used in an API-ledapproach to connectivity fall into three categories:
System APIs - these usually access the core systems of record and provide a means of insulating the user from the complexity or any changes to the underlying systems. Once built, many users, can access data without any need to learn the underlying systems and can reuse these APIs in multiple projects.
Process APIs - These APIs interact with and shape data within a single system or across systems (breaking down data silos) and are created here without a dependence on the source systems from which that data originates, as well as the target channels through which that data is delivered.
Experience APIs - Experience APIs are the means by which data can be reconfigured so that it is most easily consumed by itsintended audience, all from a common data source, rather than setting up separate point-to- point integrations for each channel. An Experience API is usually created with API-first design principles where the API is designed for the specific user experience in mind.

Correct answer is Save the payload from the Database SELECT operation to a variable Response from HTTP requestwill override the payload and hence response of database SELECT can be lost.
Best way to preserve is to assign payload of first operation to variable using TransformMessage.

Correct answer is Merges elements of two lists (arrays) into a single list MuleSoft Doc Reference : https://docs.mulesoft.com/mule-runtime/4.3/dw-core-functions-zip