塔压升高可能存在的原因有哪些？
参考答案：
（1）回流过大；（2）冷凝冷却器堵塞；（3）溢流管堵塞；（4）进料量过大；（5）原料带水。
学校图书馆科技书占图书总数的40%，故事书占图书总数的30%，故事书比科技书少1200本，科技书有多少本？
This machine _____. It hasn't worked for years. [ ]
A. didn't work
B. wasn't working
C. doesn't work
D. isn't working
