English verb conjugation CAN HAPPEN
Regular verb: happen - happened - happened
Affirmation
Simple form
--
it can happen
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V-ing form
--
it can be happening
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Perfect
--
it can have happened
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V-ing perfect
--
it can have been happening
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Negation
Simple form
--
it can't happen
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V-ing form
--
it can't be happening
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Perfect
--
it can't have happened
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V-ing perfect
--
it can't have been happening
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Interrogative form
Simple form
--
can it happen?
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V-ing form
--
can it be happening?
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Perfect
--
can it have happened?
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V-ing perfect
--
can it have been happening?
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Interro-negative form
Simple form
--
can't it happen?
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V-ing form
--
can't it be happening?
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Perfect
--
can't it have happened?
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V-ing perfect
--
can't it have been happening?
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