对UTRAN Iux接口特点描述正确的是：( ) Which of the following statements about the features of the UTRAN Iux interface are correct? ( ) A.所有的接口具有开放性 All interfaces are open B.将无线网络层和传输层分离 The radio network layer is separated from the transmission layer C.控制面和用户面分离 The control plane is separated from the user plane D.Iub接口不开放，其余接口都开放 The Iub interface is not open and all other interfaces are open
