can happen
Verbo regular: happen - happened- happened

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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it can happen
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it can be happening
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it can have happened
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it can have been happening
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Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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it cannot happen
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it cannot be happening
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it cannot have happened
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it cannot have been happening
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Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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can it happen?
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can it be happening?
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can it have happened?
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can it have been happening?
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Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
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can it not happen?
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can it not be happening?
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can it not have happened?
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can it not have been happening?
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