To answer this question, you need to understand the concept of message processing and sequencing. Let's go through each option to understand why it is correct or incorrect:
Option A) Unit-or-Sort - This option is incorrect because it does not accurately describe the feature of grouping messages into a single unit that is processed sequentially.
Option B) Message Sorting - This option is incorrect because it refers to the act of arranging messages in a particular order, but it does not specifically describe the feature of grouping messages into a single unit.
Option C) Destination Keys - This option is incorrect because it does not relate to the concept of grouping messages into a single unit for sequential processing.
Option D) Unit-of-Order - This option is correct because it accurately describes the feature of grouping messages into a single unit that is processed sequentially in the order that the messages were created. This ensures that the messages are processed in the correct sequence.
The correct answer is D) Unit-of-Order. This option is correct because it accurately describes the feature mentioned in the question.