As shown in the figure, the switches all run RSTP. Initially, SWA, SWB and SWC are interconnected through links 1, 2 and 3. When the network connection undergoes the following changes, which of the following is the correct statement?

A . When the link between SWB and SWC is DOWN, both SWB and SWC will send RST BPDU with TC set.
B . As shown in the figure, when SWB is connected to another switch SWD running RSTP, SWB will send RSTBPDU with TC set.
C . As shown in the figure, when SWB is connected to another switch SWD running RSTP, SWD will send RSTBPDU with TC set.
D . When the edge port EO/1 of SWC is connected to a PC, SWC will send a RST BPDU with TC set.

Answer: B