Standard English would have closed, with a 'd' on the end; but the omission of the final consonant is common in Singapore and probably elsewhere. And there is a tendency for English teachers to wring their hands in despair at this kind of non-standard usage.On the other hand, maybe we should think about this a bit more. We can use open as both a verb and an adjective with no need to add a suffix:
Please open the door. (Verb)So why can't we do the same with close? Why do we need a suffix when it used as an adjective?
The door is already open. (Adj)
Please close the door. (Verb)In reality, there is sometimes little logic to English usage, and one's heart goes out to people struggling to learn it.
The door is already closed. (Adj)
