A:Cl-的结构示意图
B:铁红的化学式为Fe3O4
C:甲醛的结构简式:CH2O
D:CO2的电子式
撒哈拉以南非洲地区生态环境恶化的根本原因是( )
What are people supposed to do when they meet for the first time in China?( )