单项选择题

A.△t=(1-φ-Vsh)△tma +Vsh △tsh +φ(1-Shr)△tmf +φShr△thr
B.△t=(1-φ-Vsh)△tma +Vsh △tsh +φ(1-Shr)△tmf
C.△t=(1-φ-Vsh)△tma +Vsh △tsh
D.△t=(1-φ-Vsh)△tma +Vsh △tsh +φ(1-Shr)