Ted told his father he ______ his homework three hours before.

A．finished

B．has finished

C．was finishing

D．had finished

已知某酶的Km为0．05mmol／L，要使此酶的反应速度达最大反应速度的80％，底物浓度应为（）.

A.0.1mmol／L

B.0.2mmol／L

C.0.3mmol／L

D.0.4mmol／L

E.0.5mmol／L