Afirmação
Forma simple
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it could freeze
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Forma com V-ing
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it could be freezing
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Perfeito
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it could have frozen
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Perfeito com V-ing
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it could have been freezing
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Negação
Forma simple
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it could not freeze
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Forma com V-ing
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it could not be freezing
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Perfeito
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it could not have frozen
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Perfeito com V-ing
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it could not have been freezing
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Forma interrogativa
Forma simple
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could it freeze?
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Forma com V-ing
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could it be freezing?
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Perfeito
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could it have frozen?
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Perfeito com V-ing
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could it have been freezing?
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Forma interro-Negação
Forma simple
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could it not freeze?
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Forma com V-ing
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could it not be freezing?
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Perfeito
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could it not have frozen?
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Perfeito com V-ing
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could it not have been freezing?
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