Which two statements are true regarding subqueries?

Which two statements are true regarding subqueries? (Choose two.)

A.
A subquery can retrieve zero or more rows.

B.
Only two subqueries can be placed at one level.

C.
A subquery can be used only in SQL query statements.

D.
A subquery can appear on either side of a comparison operator.

E.
There is no limit on the number of subquery levels in the WHERE clause of a SELECT statement.