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：考查非谓语动词的用法。根据题意可知，这里应用动词不定式表示目的。句意为：为了提高工作效率，老板同意职工喝杯咖啡休息一下。