—What would I do if I can't sleep before a big exam?          

—You'd better            a long walk before going to bed.               [ ]

A. take              

B. taking                

C. to take

不受位阻效应影响，更易发挥生物素活性作用的是（）

A.BCNHS

B.BCHZ

C.BHZ

D.光生物素

E.生物素脱氧核苷三磷酸