气相色谱法测定氯苯时，氯苯标准工作液需临用现配。
参考答案：对
Which of the following are NOT considered important in defining an urban area
A．Political boundaries.
B．Transportation networks.
C．Social relationships.
D．Economic systems.
在以下逻辑运算中，属于扩大检索范围，增加命中文献篇数，提高查全率的运算是（）
A、逻辑“与”
B、截词
C、逻辑“或”
D、算符优先
