题目

— Has Yang Liping returned from Yunnan yet? I’d like to meet her.    — Sorry. She _______ back here only for last weekend. A. has been        B. would be             C. had been          D. was 答案：D14．实验室用如图所示装置制备乙酸乙酯．（1）试管a中生成乙酸乙酯的化学方程式是CH3COOH+C2H5OH$?_{△}^{浓H_{2}SO_{4}}$CH3COOC2H5+H2O．下列说明该反应已经达到化学平衡状态的是ad．a．正、逆反应速率相等b．C、D、E的浓度均相等c．体系的质量不再发生变化d．C、D、E的质量均不再变化（2）试管a中试剂的添加顺序是先加入乙醇，再加入浓硫酸，最后加入乙酸．（3）试管b中盛放的试剂是饱和碳酸钠溶液，导气管不伸入液面下的理由是防止倒吸．