The command show route receive-protocol bgp is the correct tool to verify the routes being advertised by a BGP peer before they are processed by the local router's import policies. This command displays the BGP path attributes, including the AS path, for all prefixes received from that neighbor. This directly allows an administrator to see that the 0.0.0.0/0 route is "coming from AS 64512" as it was advertised. While the exhibit shows the route after it has been selected and installed in the inet.0 routing table, the receive-protocol command is the specific function to inspect the raw advertisements from a peer.

B. show route protocol bgp source-gateway is not a valid command syntax in the Junos OS.

C. show route protocol bgp next-hop is not a valid command syntax in the Junos OS.

D. The hidden keyword is used to display received routes that are not considered for path selection (e.g., due to an invalid next-hop). The route in the exhibit is active, as indicated by the asterisk (), not hidden.

1. Juniper Networks TechLibrary - show route receive-protocol: "Use this command to display the routes that a BGP routing device has received from a neighbor, before the routing policy is applied." This documentation confirms that this command is used to inspect incoming advertisements from a peer, which includes the AS path attribute. (Source: Juniper Networks TechLibrary, CLI Explorer, show route receive-protocol).

2. Juniper Networks TechLibrary - show route: The documentation for the show route command and its variants (show route protocol bgp) does not list source-gateway or next-hop as valid keywords, confirming options B and C are incorrect. The hidden option is described for displaying routes that are not eligible to become active. (Source: Juniper Networks TechLibrary, CLI Explorer, show route).

3. Junos Routing Protocols Configuration Guide - Monitoring BGP: This guide details the use of operational mode commands for BGP. It specifies show route receive-protocol bgp peer-address as the method to "View the routes that the local router has received from the BGP peer before the routing policy has been applied." (Source: Junos OS 22.4, Routing Protocols Configuration Guide, Section: "Monitoring BGP Configuration and Operation").