What is the answer to this question with this change: the 4th transmission (B sends to D) does not occur

2.7.0 Suppose we have the Ethernet switches S1 through S4 arranged as below. All forwarding tables are empty; each switch uses the learning algorithm of 2.4 Ethernet Switches. 54 S2 53 Now suppose the following packet transmissions take place: .A sends to D D sends to A .A sends to B B sends to D For each switch S1-S4, list what source addresses (eg A,B,C,D) it has seen (and thus what nodes it has learned the location 0