may happen
Regular verb: happen - happened- happened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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it may happen
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it may be happening
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it may have happened
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it may have been happening
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Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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it may not happen
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it may not be happening
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it may not have happened
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it may not have been happening
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Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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may it happen?
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may it be happening?
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may it have happened?
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may it have been happening?
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Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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may it not happen?
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may it not be happening?
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may it not have happened?
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may it not have been happening?
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