What is true regarding sub queries?

A.
The inner query always sorts the results of the outer query

B.
The outer query always sorts the results of the inner query

C.
The outer query must return a value to the outer query

D.
The inner query returns a value to the outer query

E.
The inner query must always return a value or the outer query will give an error

Explanation:
The inner query returns a value to the outer query.
If the inner query does not return a value, the outer query does not return a result