Which sequence of characters introduces an ABAP Doc comment?

The correct sequence of characters that introduces an ABAP Doc comment is the exclamation mark "!". In ABAP, comments can be added to the code for clarity and documentation purposes, and the exclamation mark specifically allows for the creation of ABAP Doc comments. These comments are intended to document the code in a way that can be processed by certain documentation tools, enabling developers to generate helpful documentation automatically from the source code.

ABAP Doc comments are more than just ordinary comments; they can include metadata that describes the functionality of the code, making them very useful when sharing code within teams or for future reference. Utilizing this comment structure ensures that the documentation is clear and can be utilized by documentation generation tools.

The other characters, while they may indicate comment structures in some contexts (like "#" for standard comments), they do not create ABAP Doc comments specifically. Hence, the exclamation mark is the appropriate choice for this context.