could corroborate
Regular verb: corroborate - corroborated- corroborated

Affirmation 	
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I could corroborate
you could corroborate
he could corroborate
we could corroborate
you could corroborate
they could corroborate 	I could be corroborating
you could be corroborating
he could be corroborating
we could be corroborating
you could be corroborating
they could be corroborating	I could have corroborated
you could have corroborated
he could have corroborated
we could have corroborated
you could have corroborated
they could have corroborated	I could have been corroborating
you could have been corroborating
he could have been corroborating
we could have been corroborating
you could have been corroborating
they could have been corroborating	

Negation 	
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I couldn't corroborate
you couldn't corroborate
he couldn't corroborate
we couldn't corroborate
you couldn't corroborate
they couldn't corroborate 	I couldn't be corroborating
you couldn't be corroborating
he couldn't be corroborating
we couldn't be corroborating
you couldn't be corroborating
they couldn't be corroborating	I couldn't have corroborated
you couldn't have corroborated
he couldn't have corroborated
we couldn't have corroborated
you couldn't have corroborated
they couldn't have corroborated	I couldn't have been corroborating
you couldn't have been corroborating
he couldn't have been corroborating
we couldn't have been corroborating
you couldn't have been corroborating
they couldn't have been corroborating	

Interrogative form 	
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could I corroborate?
could you corroborate?
could he corroborate?
could we corroborate?
could you corroborate?
could they corroborate? 	could I be corroborating?
could you be corroborating?
could he be corroborating?
could we be corroborating?
could you be corroborating?
could they be corroborating? 	could I have corroborated?
could you have corroborated?
could he have corroborated?
could we have corroborated?
could you have corroborated?
could they have corroborated? 	could I have been corroborating?
could you have been corroborating?
could he have been corroborating?
could we have been corroborating?
could you have been corroborating?
could they have been corroborating? 	

Interro-negative form 	
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couldn't I corroborate?
couldn't you corroborate?
couldn't he corroborate?
couldn't we corroborate?
couldn't you corroborate?
couldn't they corroborate? 	couldn't I be corroborating?
couldn't you be corroborating?
couldn't he be corroborating?
couldn't we be corroborating?
couldn't you be corroborating?
couldn't they be corroborating? 	couldn't I have corroborated?
couldn't you have corroborated?
couldn't he have corroborated?
couldn't we have corroborated?
couldn't you have corroborated?
couldn't they have corroborated? 	couldn't I have been corroborating?
couldn't you have been corroborating?
couldn't he have been corroborating?
couldn't we have been corroborating?
couldn't you have been corroborating?
couldn't they have been corroborating?