Refer to the exhibit. In this BGP setup, 10.1.1.0/24 is advertised by AS 400 to its peers. Border routers in AS 100 reset the next-hop router to themselves. R2, R3, and R4 are route reflector clients

R1 is the route reflector and does not reset the BGP next-hop attribute when reflecting routes to iBGP peers, so R1 would not appear as the next-hop on R5.

R2 is a route reflector client, not the border router that received the prefix from AS 400 and reset the next-hop, so it would not be the next-hop seen by R5.

R3 is a route reflector client, not the border router that received the prefix from AS 400 and reset the next-hop, so it would not be the next-hop seen by R5.

In BGP route reflection, a route reflector (R1) does not modify the next-hop attribute when reflecting routes to clients or non-client iBGP peers. R4, as the border router that received 10.1.1.0/24 from AS 400, reset the next-hop to itself per the configured policy. When R1 reflects this route to R5 (a non-client peer), the next-hop remains R4, making D the correct answer.

R6 is in an external AS and while it originated the route, the border routers in AS 100 explicitly reset the next-hop to themselves, so R6 would not be the next-hop within AS 100.