对于SN添加流程说法正确的是：
A满足B1事件门限，UE上报B1测量报告。MeNB向SN发送Sn Addition Request消息
BMeNB给UE下发NR测量配置，包含B1事件门限
CMeNB收到SgNB的SgNB Addition Request Acknowledge消息后，下发空口RRC Connection Reconfiguration消息给UE,携带SgNB侧的SCG配置
DSgNB接收到SgNB Addition Request消息后，Pscell候选小区选择和接纳控制，接纳成功给MeNB回复SgNB Addition Request Acknowledge消息