完成A接口倒换后，BSC出现2992错误（BTS AND TC UNSYNCHRONIZATION CLEAR CALLS ON A INTERFACE alarm），说明A接口可能存在哪类问题（）

• A、A interface exist crossconnect circuit
• B、inconsistent CCSPCM between BSC and MSC
• C、A interface exist loop circuit
• D、inconsistent circuit number in circuit group between BSC and MSC