Which two statements are true about optical networks?（）
- A、SONET and SDH both use time-division multiplexing.
- B、An optical transport network system uses time-division multiplexing.
- C、SONET and SDH both use wavelength-division multiplexing.
- D、An optical transport network system uses wavelength-division multiplexing.
正确答案:A,D
答案解析:有
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