A:Mg2+、Al3+、Fe2+
B:H+、Mg2+、Al3+
C:H+、Ba2+、Al3+
D:只有Mg2+、Al3+
已知13.5亿是由四舍五入取得的近似数,它精确到( )
—Is first impression very important?
—Yes, it is, because you never get second chance to make first impression.