问题：

[多选] Which three statements about subqueries are true? （）

A . A main query can have more than one subquery.
B . A subquery can have more than one main query.
C . The subquery and main query must retrieve data from the same table.
D . The subquery and main query can retrieve data from different tables.
E . Only one column or expression can be compared between the subquery and main query.
F . Multiple columns or expression can be compared between the subquery and main query.