1.They were completely unable to maintain discipline.
她们完全不能维持纪律。
2.In the past, Opec's members have struggled to maintain discipline on lower production quotas during periods of falling oil prices.
过去,在油价下跌期间,欧佩克成员国总是难以遵守减产配额规定。
3.upon the teacher to maintain discipline.
教师有责任维护纪律。