Which of the following is NOT a valid technique to control deadlocks?

a$.$ Deadlock detection: the DBMS periodically tests the database for deadlocks.

b$.$ Deadlock abortion: all transactions are aborted for the requested object.

c$.$ Deadlock avoidance: the transaction must obtain all of the locks it needs before it can be executed.

d$.$ Deadlock prevention: a transaction requesting a new lock is aborted when there is the possibility that a deadlock can occur.