第一次亮相的关键在于导游人员的仪容、仪表和使用的语言。()
A．正确
B．错误
参考答案：对
21×42+21×63-21×5=______．
One of the main advantages of a graphite-furnace atomizer is that（）
A.It requires only very small quantities of a sample
B.It requires metal.ions in aqueous solution
C.It does not produce background emission like a flame
D.It does not get hot like a flame
