BGP is the standard routing protocol commonly used in the Internet to exchange routing and reachability information between two or more networks. BGP enables the Azure VPN Gateways and your on-premises VPN devices, called BGP peers or neighbors, to exchange "routes" that will inform both gateways on the availability and reachability for those prefixes to go through the gateways or routers involved. BGP can also enable transit routing among multiple networks by propagating routes a BGP gateway learns from one BGP peer to all other BGP peers.
Incorrect:
Not C: A VPN gateway must have a Public IP address. Verify that you have an externally facing public IPv4 address for your VPN device.
Reference:
https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-bgp-resource-manager-ps
https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-howto-site-to-site-resource-manager-cli