For/Since/During/While
For:
Used to express a complete duration of time.
ex. I have been walking for 2 hours.
Since:
Used when the beginning of the duration is what is important.
ex. I have been working here since April.
During
Used when 2 actions happen at the same time and the second action is a duration expressed in a noun.
ex. I fell asleep during English class.
While
Used when 2 actions happen at the same time and they are both expressed as verbs.
ex. I met him on the street while I was walking.
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