______, Franks never seems to be able to do the work satisfactorily. [ ]

A. As hard he tries

B. Try hard as he might

C. As hard as he tries

D. Try as hard as he might

下列有关Km值的叙述，哪项错误（）

A.Km值是酶的特征性常数

B.Km值是达到最大反应速度一半时的底物浓度

C.它与酶对底物的亲和力有关

D.Km值最大的底物，是酶的最适底物

E.同一酶作用于不同底物，则有不同的Km值