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

从晶体结构的变化来看，同质多像转变又可分为（）。

A.移位型转变

B.重建型转变

C.型变

D.有序－无序转变