Carbon dioxide______from burning fuels is the most common of the so-called green house gases.[      ]

A. producing        

B. having been produced  

C. to be produced        

D. produced

急性再生障碍性贫血时贫血发生常是由于（）

A.红细胞生成素缺乏

B.免疫机制

C.原位溶血

D.失血

E.红细胞本身缺陷