Refer to the exhibit． What switch proves the spanning-tree designated port role for the network segment that services the printers?

【正确答案】 C

【答案解析】题目求哪一个交换机为打印机提供指定端口？
由图可知S1是根桥。指定端口是基于网段间选举的。
S3--S4之间S3的BID比S4小，所以S3-S4之间的指定端口在S3上。