Which two statements are true regarding sub queries?

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

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

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

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

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

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