their service, the workers of the hotel are active in learning English.
A. Improving
B. To improve
C. Improve
D. Having improved
网友回答
A. Improving
(答案→)B. To improve
C. Improve
D. Having improved
解析：考查非谓语动词。句意：为了提高他们服务水平，这些旅馆的工人正在积极地学习英语。不定式表示具体的将要进行的动作，结合语境可知选B。