39. The president promised to keep all the board members ______ of how the talks were going on.
A. inform
B. informing
C. be informed
D. informed

解析：
该题考查的是固定短语，固定搭配。
keep someone informed of...：告知某人……
所以选D。
参考译文：
总裁承诺会把谈判的进展告知所有的董事会成员。
其他语言点：
promise：n. / v. 承诺；promise to do something：承诺做某事；make a promise：许诺
宾语从句：“how the talks were going on”是how引导的宾语从句（充当of的宾语）