Complete the following sentence with a (compound) word derived from the one(s) given in bracket.
John's brother has been working in a United Nations （ ）(keep,peace)force.
【正确答案】：PEACEKEEPING
【题目解析】：
约翰的兄弟一直在联合国维和部队工作。United Nations Peacekeeping Force（联合国维持和平部队），固定用法。