Which of the following are valid ways to insert a comment in a Data Definition (DDL source)?

The valid ways to insert a comment in a Data Definition Language (DDL) source with respect to ABAP programming involve specific syntax conventions that ensure the comments are properly recognized by the ABAP compiler.

The first option uses double slashes, which is not a standard method for ABAP comments. In ABAP, comments are typically indicated through other established notations.

The second option, using the /* comment */ syntax, is indeed a correct way to add multi-line comments in ABAP, allowing for detailed explanations or annotations that can span multiple lines. This method is widely used in programming languages for commenting out code blocks or providing longer descriptions.

The third option employs an asterisk at the beginning of the line, which is a recognized method to insert comments in ABAP. This style is particularly common in report programs and allows for single-line comments effectively.

The last option uses double hyphens, which is not used for comments in ABAP. Instead, this syntax is found in many SQL query languages for marking comments.

Therefore, the correct answer highlights the accepted commenting styles in ABAP, specifically pointing out the functionality of the multi-line comment syntax and the single-line comment format with an asterisk, which are critical for documenting and maintaining code in ABAP