A.同時傳遞數(shù)據(jù)語音且上下數(shù)據(jù)帶寬對稱 B.同時傳遞數(shù)據(jù)語音且上下數(shù)據(jù)帶寬不對稱 C.只傳數(shù)據(jù)上下對稱 D.只傳數(shù)據(jù)上下不對稱