A cicular plasmid of 10,000 base pairs (bp) is digested with two restrication enzymes, A and B , to produce a 3000 bp and a 2000 bp bands when visualized on an agarose gel. When digested with one enxyme at a time only one band is visible at 5000 bp. If the first site for enzyme a(A1) is present at the `100^(th)` base, the order in which the remaining sites (A2,B1 and B2 ) are present is-