the working efficiency the boss allows the employees to have a coffee break. A. Improving

问题补充：

the working efficiency, the boss allows the employees to have a coffee break.

A. Improving

B. To improve

C. Having improved

D. Improved

答案：

A. Improving

(答案→)B. To improve

C. Having improved

D. Improved

解析：考查不定式做目的状语，句意是：为了提高工作效率，老师允许职员喝杯咖啡休息一下。选A。