Which two statements are true regarding sub queries?

Which two statements are true regarding sub queries? (Choose two.)

A.
A sub query can retrieve zero or more rows.

B.
Only two sub queries can be placed at one level.

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

D.
A sub query can appeal* on either side of a comparison operator.

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