不加“s"是指具体的那一年，如果加“s”是指年代，前面有the哦比如the 1970s是20世纪70年代，希望你可以明白.
It was many years before the full story was made public.
许多年之后，事情的全貌才公之于众。
The new tax will be phased in over two years.
新税种将在两年内逐步实行。
The company has come a long way in the last 5 years.
公司在过去的5年里取得了许多进步。
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