The manager says that the project is progressing smoothly,and that all construction work________by

the end of next month. [ ]

A. has been completed  

B. has completed

C. will have been completed  

D. will have completed

下列各组化合物中，铁元素的质量分数按由低到高的顺序排列的是（　　）

A．FeO、Fe₂O₃、Fe₃O₄、FeS₂

B．FeS₂、Fe₂O₃、Fe₃O₄、FeO

C．FeO、Fe₃O₄、Fe₂O₃、FeS₂

D．FeS₂、FeO、Fe₂O₃、Fe₃O₄