单项选择题 Hardware networking devices operate within the protocol stack just like protocols them-selves.Thus，hardware networking devices can be associated with an OSI model layerrelated to the protocols they manage or control.At which layer of the OSI model does arouter operate？（）

单项选择题 Unfortunately，attackers have many options of attacks to perform against their targets. Which of the following is considered a denial-of-service （DoS）attack？（）

单项选择题 Some adversaries use DoS attacks as their primary weapon to harm targets，whereas othersmay use them as weapons of last resort when all other attempts to intrude on a target fail. Which of the following is most likely to detect DoS attacks？（）