A. Sql doesn't eliminate duplicate rows like relational algebra.to eliminate duplicate row we need to use DISTINCT keyword with SELECT in SQL
B. Every table requires a primary key for performance. If you don’t have a primary key in any table, your tables don’t follow standard SQL requirements and performance suffers. Primary keys are automatically set as clustered indexes, which speeds up queries. They are always unique, so you can use an auto-incremented numeric value if you have no other column in the table that meets the unique requirement.
C. SQL not permits attributes names to be repeatedin the same relation
Therefore option D is correct.