【单选题】
How many broadcast domains are shown in the graphic assuming only the default vlan is configured on the switches?()<br /> <img src="https://nimg.ppkao.com/2018-07/zhanglijun/2018072317285690760.jpg?sign=41c21d160dd44f1045ded1c930f3f3ba&t=62d196ee" />
A、one
B、six
C、twelve
D、two