A.增加 B.減少 C.不變 D.增加或減少
A.(TH+TL)/TH B.TH/(TH-TL) C.TL/(TH-TL) D.(TL-TH)/TH
A.ηt>0 B.0<ηt<1 C.ηt≤1 D.ηt<0