四级试剂又叫（）。
A、优级纯
B、实验纯
C、分析纯
D、化学纯
参考答案：B
吸毒正成为全球性严重的社会问题，青少年应自觉拒绝毒品．______．
More than one（）the people heart and soul.
A. official has served
B. officials have served
C. official has served for
D. officials have served for
