Which statement is true regarding subqueries?（）

A.Only one LONG column can be used per table 
B.A TIMESTAMP data type column stores only time values with fractional seconds 
C.The BLOB data type column is used to store binary data in an operating system file 
D.The minimum column width that can be specified for a VARCHAR2 data type column is one 
E.The value for a CHAR data type column is blank-padded to the maximum defined column width

A.A subquery can retrieve zero or more rows 
B.Only two subqueries can be placed atone 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 

A.They accept only a single argument 
B.They can be nested only to two levels 
C.Arguments can only be column values or constants 
D.They always return a single result row for every row of a queried table 
E.They can return a data type value different from the one that is referenced