the working efficiency，the boss allows the employees to have a coffee break.
A. Improving
B. To improve
C. Having improved
D. Improved
网友回答
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。