单选题：The four necessary deadlock conditions are mutual exclusion, ___

The four necessary deadlock conditions are mutual exclusion, _______, non preemption, and circular wait. @[B](1)
A. Block and wait
B. Hold and wait
C. Release and wait
D. Release and block





A.Block and wait
B.Hold and wait
C.Release and wait
D.Release and block


答案：B