A is correct because the interface is configured as a disabled port. A disabled port does not forward any traffic, including DHCP packets. Therefore, DHCP snooping cannot learn any MAC addresses or lease information from a disabled port.
C is correct because the interface is configured as a trunk port. By default, all trunk ports on the switch are trusted for DHCP snooping. This means that DHCP snooping does not inspect or filter any DHCP packets received on a trunk port. Therefore, DHCP snooping does not add any entries to the snooping database for a trunk port.

Switch A is already fixed as the root bridge in this topology (priority 0), so the outcome being engineered here is not about root bridge election at all, but about which of Switch C's two available paths toward that already- established root - the direct C-to-A link, or the indirect C-to-B-to-A path - RSTP selects as the lower-cost, primary path. RSTP's path-cost calculation for any non-root switch sums the port costs of every link along a candidate path to the root and always selects whichever candidate path has the lowest total accumulated cost as that switch's active root path, placing the corresponding local port into the forwarding root port role while any higher-cost alternative path is placed into a non-forwarding (alternate) role. To force Switch C to prefer routing through Switch B rather than connecting to Switch A directly, the administrator must make the direct C-to-A link's cost higher than the combined cost of the C-to-B link plus the B-to-A link added together, so that the indirect, two-hop path through Switch B mathematically totals to a lower cumulative cost than the single direct hop, causing RSTP's cost comparison to favor the indirect path as primary. Setting Switch B's priority (to either 1 or 0) is irrelevant here, since Switch B is not a root bridge candidate in this scenario and priority manipulation would only affect a root bridge election, not path cost preference between a fixed root and a downstream switch. Lowering the direct link's cost, the inverse of the correct answer, would instead reinforce the direct path rather than override it. Reference topics: Junos Enterprise Switching - Spanning Tree Protocols, RSTP Path Cost and Root Port Selection.

The exhibit shows the configuration of RSTP on EX-4, which has the command force-version stp.
This command forces the switch to use the legacy STP protocol instead of RSTP, even though the switch supports RSTP. This means that EX-4 will not be able to take advantage of the faster convergence and enhanced features of RSTP, such as edge ports, link type, and proposal/agreement sequence. The other switches in the network are likely to be running RSTP, as it is the default protocol for EX Series switches. Therefore, there will be a compatibility issue between EX-4 and the other switches, which will result in longer convergence times and suboptimal performance. The switch will also generate a warning message that says "Warning:
STP version mismatch with neighbor" when it receives a BPDU from a RSTP neighbor.
To solve this problem, the force-version command must be removed from EX-4, so that it can run RSTP natively and interoperate with the other switches in the network. This will enable faster convergence and better stability for the network topology. To remove the command, you can use the delete protocols rstp force-version command in configuration mode.

BGP employs two distinct loop-prevention mechanisms depending on whether peers are external or internal to the same autonomous system. Between external peers (EBGP), loop prevention relies on the AS path attribute: every time a route crosses an AS boundary, the local AS number is prepended to the path, and a router rejects any incoming route whose AS path already contains its own AS number, since that would indicate the route has looped back around. Between internal peers (IBGP) within the same AS, however, the AS path attribute never changes, because IBGP does not add AS numbers as routes are readvertised internally
- meaning AS path alone cannot detect an internal loop. Instead, IBGP enforces a strict split-horizon-style rule: a router that learns a route via IBGP must never readvertise that route to another IBGP peer. This rule guarantees that every IBGP speaker within the AS must be directly peered with every other IBGP speaker (a logical full mesh) in order for all routers to receive all routes, since no IBGP router will relay IBGP-learned routes onward on another router's behalf. This full-mesh requirement is precisely why techniques such as route reflection and confederations were later developed - they preserve the same loop-prevention guarantee while relaxing the physical full-mesh peering burden. VRRP and BFD serve entirely unrelated purposes (gateway redundancy and fast failure detection, respectively) and play no role in BGP loop prevention.
Reference topics: Junos Enterprise Routing - BGP, IBGP Split-Horizon and the Full-Mesh Requirement.