could happen
Verbo regolare: happen - happened- happened

Affermazione 	
Forma semplice 	Forma con V-ing 	Perfetto 	Perfetto con V-ing 	
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it could happen
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it could be happening
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it could have happened
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it could have been happening
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Negazione 	
Forma semplice 	Forma con V-ing 	Perfetto 	Perfetto con V-ing 	
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it couldn't happen
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it couldn't be happening
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it couldn't have happened
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it couldn't have been happening
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Forma interrogativa 	
Forma semplice 	Forma con V-ing 	Perfetto 	Perfetto con V-ing 	
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could it happen?
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could it be happening?
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could it have happened?
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could it have been happening?
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Forma interro-negativa 	
Forma semplice 	Forma con V-ing 	Perfetto 	Perfetto con V-ing 	
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couldn't it happen?
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couldn't it be happening?
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couldn't it have happened?
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couldn't it have been happening?
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