[译] 他们按预定计划完成了任务。
[误] They accomplished their task according to the schedule.

[正] They accomplished their task according to schedule.
[注] 表示“按预定计划”，应该说 according to schedule，其中在 schedule 前没有定冠词。类似的还有 ahead of schedule (提前），behind schedule（落后于预定计划或时间），on schedule（按照预定计划）等。