足球运动员用500N的力踢球。足球离开运动员的脚后又向前运动了50m，在此运动过程中，运动员对足球做的功是____________J。
0
News reports say peace talks between the two countries _____ with no agreement reached. [ ]
A. have broken down
B. have broken out
C. have broken in
D. have broken up
简述企业利润预测的方法。
