Considering that Aggregates can have hidden columns, which of the following options is correct?

Considering that Aggregates can have hidden columns, which of the following options is correct?
A . The hidden columns help optimizing the Aggregate.
B. Columns that are empty in the database are automatically hidden.
C. The hidden columns are not part of the output.
D. Hiding columns in the Aggregate only affects the preview of the output.

Answer: D