Ⅱ型呼吸衰竭的血气诊断标准是

A.PaO<50mmHg,PaCO>50mmHg

B.PaO<50mmHg,PaCO>60mmHg

C.PaO<60mmHg,PaCO>50mmHg

D.PaO<40mmHg,PaCO>40mmHg

E.PaO<70mmHg,PaCO>55mmHg