You must keep us of how things are going here.
A. informing
B. informed
C. inform
D. to inform
网友回答
A. informing
(答案→)B. informed
C. inform
D. to inform
解析：考查固定搭配。inform sb of sth通知某人某事；inform sb to do sth/that通知某人做某事；keep sb informed of sth让某人知晓......。句意：你必须让我们知晓事情的发展状况。故选B。