Sam has been appointed ______ manager of the engineering department to take ______ place of

George.     [ ]  

A. /; /    

B. the; /      

C. the; the    

D. /; the

生物固氮中的固氮酶是由下列哪两个亚基组成（）

A.Mo-Fe蛋白，Fe蛋白

B.Fe-S蛋白，Fd

C.Mo-Fe蛋白，Cytc

D.Cytc，Fd