A. Network traffic is possible between VPC-Shared instances and VPC-Dept1 and VPC-Dept2 instances as long as the appropriate routes and security groups are in place, but only for communication that is initiated from VPC1-Shared instances as the default peering bi-directional communication flag has been disabled.
B. Instances within VPC-Dept1 can communicate directly with instances in VPC-Shared, as long as the appropriate routes and security groups are in place, and vice versa regardless of who initiates communication
C. All network communication remains blocked between all VPCs until the respective peering bi-directional communication flags are set to the appropriate setting that allows traffic to flow.
D. Network traffic is possible between VPC-Shared instances and VPC-Dept1 and VPC-Dept2 instances as long as the appropriate routes and security groups are in place, but only for communication that is initiated from VPC1-Shared instances as the default peering bi-directional communication flag has been enabled.