以下关于吡啶说法正确的是
A. 六个原子形成6个π电子的闭合共轭体系，芳香性比苯差
B. 亲电取代反应比苯更难。
C. 亲核取代反应比苯容易进行。
D. 以上都对
根据结构中环的情况，杂环化合物可分为
A. 单杂环
B. 稠杂环
C. 苯稠杂环
D. 杂稠杂环
[音频]
A. Call the secretary again at 10 days.
B. Make another appointment.
C. Express his thanks for the call.
D. Cancel the meeting with the secretary?
[音频]
A. She will buy another calculator.
B. She wants the man to buy a calculator.
C. She will give the man a calculator for a coffee.
D. She wants to invite the man for a coffee.
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