Which is the correct description of SQL profiling while using SQL Tuning Advisor?

Which is the correct description of SQL profiling while using SQL Tuning Advisor?

A.
It is a set of recommendations by the optimizer to create new indexes.

B.
It is auxiliary information collected by the optimizer for a SQL statement to eliminate estimation error.

C.
It is a set of recommendations by the optimizer to refresh stale statistics to avoid bad execution plan.

D.
It is a set of recommendations by the optimizer to restructure a SQL statement to avoid bad execution plan.