题干
When the peace talks _______, they realized that there would be a war between the two countries.
A：broke out
B：broke u
C：broke away
D：broke dow
答案(点此获取答案解析）
D
目标函数z＝y－ax(a∈R)，若z取最大值时的唯一最优解是(1,3)，则实数a的取值范围是
