Explanation
The following are the explanations for each action:
A: Renaming a field in a structure that is included in the table definition causes an indirect change to the database table, as the field name in the table is derived from the structure. This change requires a table conversion, as the existing data in the table must be copied to a new table with the new field name, and the old table must be deleted.
B: Changing the field labels of a data element that is used in the table definition does not cause an indirect change to the database table, as the field labels are only used for documentation and display purposes. This change does not require a table conversion, as the existing data in the table is not affected by the change.
C: Deleting a field from a structure that is included in the table definition causes an indirect change to the database table, as the field is removed from the table as well. This change requires a table conversion, as the existing data in the table must be copied to a new table without the deleted field, and the old table must be deleted.
D: Shortening the length of a domain used in a data element that is used in the table definition causes an indirect change to the database table, as the field length in the table is derived from the domain. This change requires a table conversion, as the existing data in the table must be checked for compatibility with the new field length, and any data that exceeds the new length must be truncated or rejected.
References: Converting Database Tables - ABAP Keyword Documentation, Adjustment of Database Structures - ABAP Keyword Documentation