SQL data definition commands make up a(n) ________ .

Option A: DDL - DDL stands for Data Definition Language. It consists of SQL commands used to define the database structure, such as creating and modifying tables, indexes, views, etc.
Option B: DML - DML stands for Data Manipulation Language. It consists of SQL commands used to manage data within the database, such as inserting, updating, deleting data.
Option C: HTML - HTML is not related to SQL data definition commands. HTML is a markup language used for creating web pages.
Option D: XML - XML is not related to SQL data definition commands. XML is a markup language used for encoding documents in a format that is both human-readable and machine-readable.
Conclusion:
SQL data definition commands, such as creating tables and defining their structure, are part of the Data Definition Language (DDL). Therefore, the correct answer is Option A: DDL.