一个国家在激烈的国际竞争中取胜的关键是（）。
计算机软件分为哪些软件？各自的作用是什么？
Which of the following statements concerning IGMP are correct？（Choose all that apply.）（） ["With IGMPvl， queries are sent to a specific group","Hosts issuing IGMPvl requests will be correctly interpreted by IGMPv2 hosts due to backwardcompatibility","An IGMPv2 router will ignore IGMPv2 leave messages when IGMFVl hosts are present","With IGMFV2， a leave message is supported","An IGMPv2 host will send an IGMFVl report on an IGMFVl router","An IGMPv2 router can only allow IGMPv2 hosts to execute a join request"]
注册号的编排方式为×（×）1（食）药监械（×2）字××××3第×4××5××××6号。其中：×1 为（） ["注册审批部门所在地的简称","批准注册年份","产品管理类别","产品品种编码"]
沃克环流
光纤有什么特点？
