Choose the correct word from the given options, to fill in the blank…

The correct answer is Option (3) → until

Complete sentence: I will stay here until you return. "Stay" names a continuing action, and "you return" is its end point. Staying here is a continuing action that goes on up to the moment of the other person's return.

Option	Meaning and use	Example
(1) when	When marks a point of time. "I will stay here when you return" says the staying begins at the return, not that it lasts up to it.	Call me when you reach home.
(2) after	After would mean the staying begins only after the return, the opposite of waiting for it.	We went out after the rain stopped.
(3) until (answer)	Until means up to the time when. It marks the point at which a continuing action stops.	Wait here until the bell rings.
(4) unless	Unless means "if not" and states a condition. The speaker would then stay only if the other person never came back, which is not the sense.	You cannot enter unless you have a pass.