SELECT operation in SQL is equivalent to

In relational algebra, the projection operation ($\Pi$) selects specific attributes (columns) from a relation and eliminates duplicate tuples by default (as relations are mathematical sets).

In SQL, the SELECT clause specifies the list of attributes to project. However, SQL operates on multiset (bag) semantics, so SELECT retains duplicate rows unless explicitly told to eliminate them using SELECT DISTINCT.

Therefore, the SQL SELECT operation corresponds to the projection operation in relational algebra, except that SELECT in SQL retains duplicates.

Hence, (D) is the correct option.