Sequences and default values in Oracle play a crucial role in providing unique values for table columns.
* Statement B is correct: When a row is inserted into ORD_ITEMS without an explicit value for ORD_NO, the ORD_NO column gets the next number from the ORD_SEQ sequence due to the DEFAULT ord_seq.nextval clause.
* Statement D is correct: If the ORD_SEQ sequence is dropped, Oracle would not be able to get the next value for ORD_NO from ORD_SEQ, and unless another default is specified, the default for ORD_NO would be NULL.
* Statements A, C, and E are incorrect for the following reasons:
* A is incorrect because the use of the sequence in the default clause of the table definition automatically grants the necessary permissions to use the sequence when inserting into the table.
* C is incorrect because the sequence is defined to cycle when it reaches its MAXVALUE and not after every 5000 numbers. It is set to cycle, but the cycling event is triggered by the MAXVALUE limit.
* E is incorrect because while a sequence is designed to produce unique numbers, if it cycles, it can potentially generate the same number again after reaching the MAXVALUE. This statement would only be true if there was no cycling.