Both options on R2 and R3 are meant to advertise the routes that have the same AS origin as the peer, only that with as-override the AS is replaced by the one on R2/R3 before advertising

AD is correct.

A and D

advertise-peer-as is explained in: https://www.juniper.net/documentation/us/en/software/junos/routing-policy/bgp/topics/example/bgp-advertise-peer-as.html Both advertise-peer-as and as-override are BGP settings applied on the PE, not the CE, therefore the correct answer is A and D

A,D are correct.

The advertise-peer-as parameter allows a router to advertise its peer's AS number as part of the AS path attribute when sending BGP updates to other peers. This parameter is useful when two routers in the same AS need to exchange routes through another AS, such as in the case of R1 and R4. By configuring this parameter on R1 and R4, they can advertise each other's AS number to R2 and R3, respectively. The as-override parameter allows a router to replace the AS number of its peer with its own AS number when receiving BGP updates from that peer. This parameter is useful when two routers in different AS need to exchange routes through another AS that has the same AS number as one of them, such as in the case of R2 and R3. By configuring this parameter on R2 and R3, they can override the AS number of R1 and R4 with their own AS number when sending BGP updates to each other.