Which of the following is valid SQL for an Index?

Option A: CREATE INDEX ID; - This option is correct. The CREATE INDEX statement in SQL is used to create an index on a table.
Option B: CHANGE INDEX ID; - There is no standard SQL command called CHANGE INDEX. This option is incorrect.
Option C: ADD INDEX ID; - There is no standard SQL command called ADD INDEX. This option is incorrect.
Option D: REMOVE INDEX ID; - There is no standard SQL command called REMOVE INDEX. This option is incorrect.
Conclusion:
In SQL, to create an index on a table, you use the CREATE INDEX statement followed by the index name. Therefore, the correct answer is Option A: CREATE INDEX ID;.