D.

All operations are public

Explanation:
When using XML SDK for creating custom message processors, all operations are public by default and can be used by any Mule application that imports them. There is no way to make an operation private or protected in XML SDK.

References: https://docs.mulesoft.com/mule-sdk/1.1/xml-sdk#operations

A.

If the two APIs use the same domain, the VM Connector can be leveraged

Explanation
To communicate asynchronously between two APIs deployed to a two-node on-prem cluster, the developer can use the VM Connector if the two APIs use the same domain. The VM Connector allows passing messages between different Mule applications within a single Mule runtime instance or across different instances using shared memory or persistent storage. If two APIs are deployed under the same domain, they can share resources such as VM queues and communicate asynchronously using VM Connector operations.

References:
https://docs.mulesoft.com/mule-runtime/4.3/vm-connector
https://docs.mulesoft.com/mule-runtime/4.3/shared-resources

D.

XML template file, YAML configuration file

Explanation:
To package a custom policy using the HTTP Policy Transform Extension, the developer needs to create an XML template file and a YAML configuration file. The XML template file defines the policy logic using Mule components and placeholders for user-defined properties. The YAML configuration file defines the metadata of the policy, such as its name, description, category, parameters, and dependencies.

References:
https://docs.mulesoft.com/api-manager/2.x/http-policy-transform#packaging-the-policy

B. In case of a cache it, only the HTTP Caching policy is evaluating; then the cached response is returned to the caller

C.

MUnit Extensions Maven plugin

Explanation:
To unit test modules created with XML SDK, the developer needs to use the MUnit Extensions Maven plugin. This plugin allows testing XML SDK modules using MUnit by adding a dependency to the module under test and using a custom processor tag to invoke it.

References:
https://docs.mulesoft.com/mule-sdk/1.1/xml-sdk#testing

A.

The encryption key and sensitive data should be different for each environment

Explanation:
The MuleSoft recommended method to encrypt sensitive property data is to use the Secure Properties Tool that comes with Anypoint Studio. This tool allows encrypting properties files with a secret key and then decrypting them at runtime using the same key. The encryption key and sensitive data should be different for each environment to ensure security and avoid accidental exposure of sensitive data. 

References:
https://docs.mulesoft.com/mule-runtime/4.3/secure-configuration-properties

C.

Scatter-Gather as central Saga orchestrator for all API request with compensating actions for failing routes

Explanation:
To invoke multiple HTTP APIs in parallel and roll back failed requests in sequence, the developer should use a Scatter-Gather router as a central Saga orchestrator for all API requests with compensating actions for failing routes. A Scatter-Gather router executes multiple routes concurrently and aggregates the results. A Saga orchestrator coordinates a series of actions across different services and handles failures by executing compensating actions. Therefore, using a Scatter-Gather router as a Saga orchestrator allows invoking multiple HTTP APIs in parallel and rolling back any failed requests in sequence. 

References:
https://docs.mulesoft.com/mule-runtime/4.3/scatter-gather-concept
https://docs.mulesoft.com/mule-runtime/4.3/saga

D.

Publish the gate change notification to an Anypoint MQ exchanhe.
Create different Anypoint MQ queues meant for each of the other subscribing systems.
Bind the exchange with each of the queues.

Explanation:
To achieve a publish/subscribe model using Anypoint MQ, where each system receives the same gate change notification event, the developer should publish the gate change notification to an Anypoint MQ exchange, create different Anypoint MQ queues meant for each of the other subscribing systems, and bind the exchange with each of the queues. An exchange is a message routing agent that can send messages to different queues based on predefined criteria. By binding an exchange with multiple queues, each queue receives a copy of every message sent to that exchange. Therefore, each system can subscribe to its own queue and receive every gate change notification event. 

References:
https://docs.mulesoft.com/anypoint-mq/3.x/anypoint-mq-exchanges