Use since + (a specific time) like March 31, or 9:19 a.m., or Tuesday.
Examples:
I have been studying English since 1993.
John has helped me since 10:00 this morning.
Those people have been in Europe since August.
Note: Because we are talking about a time in the past until now, we have to use have/has + past participle when we use since.
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Use for + (a length of time) like 1 day, or 3 hours, or 5 years.
Examples:
I have been studying English for 4 years.
John has helped me for 8 hours.
Those people went to Europe for 2 months.
Note: It is possible to use the past tense when you use for if the action is finished.
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