A. Circular wait is one of the necessary conditions for a deadlock to occur.
B. A Cycle in a multi-instance resource may or may not cause Deadlock. (However, A Cycle in a single-instance resource will cause Deadlock)
C. In an unsafe state, the OS can't prevent threads from requesting resources in such a way that a deadlock occurs. It is not necessary unsafe state will always lead to deadlock because processes may not request their total possible resources, and may release some resources before acquiring othes.
Ref: sp13mtv6 (berkeley.edu) Check Q1)->b)->ii)
D. In the resource-allocation graph of a system, if every edge is an assignment edge, then one of the four necessary conditions, "hold and wait" is violated. That's why there is NO DEADLOCK. The absence of at least one of the four necessary conditions implies NO DEADLOCK.
Correct Option: A, D