Which statement is not correct?

a. A transaction is a set of database operations (e.g., a consecution of SQL statements in a relational database), induced by a single user or application, that should be considered as one undividable unit of work.

b. Transactions typically exist in isolation, and cannot be executed concurrently with other transactions on the same data.

c. It should not be possible to terminate a transaction in such a way that the database remains in an inconsistent state, because some operations of a single transaction were executed successfully and others were not.

d. Recovery is the activity of ensuring that, whichever problem occurred, the database is returned to a consistent state afterwards, without any data loss.