Consider these relations on the set of integers: R₁={(a,b)|a≤b}, R₂={(a,b)|a>b}, R₃={(a,b)|a=Bora=−b}, R₄={(a,b)|a=b}, R₅={(a,b)|a=b+1}, R₆={(a,b)|a+b≤3}. Which of these relations are reflexive.