每一产量点上的总成本曲线TC的斜率（）总可变成本曲线的斜率
A、等于
B、大于
C、小于
D、不确定
参考答案：A
用适当的介词填空。
1. They are staying there _____ three weeks.
2. She is leaving _____ June 15th.
3. What are they doing _____ vacation?
4. Alice is going camping _____ her classmates.
5. They are buy working now. How _____ you?
对HPLC法进行准确度考查时，回收率一般为
A．C2％B．99.7％～100.3％C．98％～102％D．1％E．0.2％
