SQL $-$ Combining Data

Which of these best describes the difference between UNION and UNION ALL in SQL$?$

UNION ALL and UNION perform the same action.

UNION ALL combines the rows from two tables, keeping only the duplicates.

UNION performs the same action but instead removes blanks.

UNION combines the rows from two tables, removing duplicates. UNION ALL performs the same action but keeps the duplicate rows.

UNION combines the columns from two tables, UNION ALL combines the columns from all available tables