In a VoIP network， which three call signaling protocols are supported by the Cisco CallManager for call setup， call maintenance， and call teardown？（） ["H323","UDP","RTP","TCP","Media Gateway Control Protocol (MGCP) ","session initiation protocol (SIP)&e"]
如何预防治安事故？
（）创立了我国第一所公立的独立幼师。 ["陈嘉庚","熊希龄","陶行知","陈鹤琴"]
下列哪些宝石为二轴晶（） ["变石","尖晶石","黄玉","绿柱石"]
文化区
细菌外毒素和内毒素有什么区别？
