I can see why you would be confused. I don't think this question is worded correctly.
I am thinking that the question should say: "which 3 routers would R1 need to peer with?".
If no-client-reflect is configured on RR1 and RR2, R1 would need to have BGP sessions with R2, and R3 so that R2 and R3 can receive the routes advertised by R1. Thus, R1 would need to peer with R2, R3, RR1 and RR2.
RR1 on the other hand, would need to peer with R1, R2, R3, and RR2 regardless of wether no-client-reflect is configured or not.