The manager promised to keep us of how our business was going on.informed B. informing C.

问题补充：

The manager promised to keep us of how our business was going on.

informed B. informing C. to inform D. havinginformed

答案：

解析：考查动词短语。固定词组:inform sb of sth通知某人某事；本题是其变化形式，keep sb informed of sth让某人知道某事。因为sb与inform之间构成被动关系，故使用过去分词的形式。句意：经理答应让我知道我们的生意进展的情况。故选A。