Explanation:
You use a CURRVAL pseudo column to look at the current value just generated from a sequence, without affecting the further values to be generated from the sequence. You use a NEXTVAL pseudo column to obtain the next possible value from a sequence by actually retrieving the value from the sequence.
Incorrect Answers:
1: You use a NEXTVAL pseudo column to obtain the next possible value from a sequence by actually retrieving the value from the sequence.
4: You use a CURRVAL pseudo column to look at the current value just generated from a sequence, without affecting the further values to be generated from the sequence.
5: This statement is not correct. There is no limitation like that in Oracle.
6: You use CYCLE clause, not REUSE, when creating a sequence to restart the sequence once it generates the maximum value defined for the sequence.
OCP Introduction to Oracle 9i: SQL Exam Guide, Jason Couchman, p. 315-322
Chapter 7: Creating Other Database Objects in Oracle

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