招标人与中标人签订合同（）个工作日内，应当向中标人和未中标的投标人退还投标保证金。
A．5
B．7
C．10
D．15
参考答案：A
— When did you see Jane?
— Last Saturday. She ______ with her sister, Lily. [ ]
A. was doing window shopping
B. did some window shopping
C. is doing window shopping
D. had done window shopping
符合802.5标准的网桥由发送帧的源结点负责路由选择，源结点发送帧时需要将详细的路由信息放在帧的首部，这类网桥被称为______。
A．第2层交换
B．网关
C．源路由网桥
D．透明网桥
