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

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：

句意为：为了提高工作效率，老板允许员工有一个喝咖啡休息的时间。不定式作目的状语，故选B项。