(1) Is a future contract American or European by nature?
(2) Can a future converge to the spot price even before expiry?
(3) Can a future contract be sold before expiry?
(1) Futures are not classified as American or European. only options are. If you are asking whether you can get out of a future contract before expiry. Yes you can.
(2) As per my understanding: Theoretically it is possible but to exactly converge will be a very rare happening.
(3) Yes.
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