原子吸收法测定金属含量最好用（）金属贮备液。
A、优级纯
B、光谱纯
C、优级纯硝酸盐
D、基准试剂硝酸盐
参考答案：B
I was afraid__________to my customers because I was afraid__________them.
A．of talking back；to lose
B．of talking back；of losing
C．to talk back；to lose
D．to talk back；of losing
种植义齿的上部结构不包括
A．人造冠
B．附着体
C．基托
D．金属支架
E．中央螺丝
