could backfill
Regular verb: backfill - backfilled- backfilled

Affirmation 	
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I could backfill
you could backfill
he could backfill
we could backfill
you could backfill
they could backfill 	I could be backfilling
you could be backfilling
he could be backfilling
we could be backfilling
you could be backfilling
they could be backfilling	I could have backfilled
you could have backfilled
he could have backfilled
we could have backfilled
you could have backfilled
they could have backfilled	I could have been backfilling
you could have been backfilling
he could have been backfilling
we could have been backfilling
you could have been backfilling
they could have been backfilling	

Negation 	
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I could not backfill
you could not backfill
he could not backfill
we could not backfill
you could not backfill
they could not backfill 	I could not be backfilling
you could not be backfilling
he could not be backfilling
we could not be backfilling
you could not be backfilling
they could not be backfilling	I could not have backfilled
you could not have backfilled
he could not have backfilled
we could not have backfilled
you could not have backfilled
they could not have backfilled	I could not have been backfilling
you could not have been backfilling
he could not have been backfilling
we could not have been backfilling
you could not have been backfilling
they could not have been backfilling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I backfill?
could you backfill?
could he backfill?
could we backfill?
could you backfill?
could they backfill? 	could I be backfilling?
could you be backfilling?
could he be backfilling?
could we be backfilling?
could you be backfilling?
could they be backfilling? 	could I have backfilled?
could you have backfilled?
could he have backfilled?
could we have backfilled?
could you have backfilled?
could they have backfilled? 	could I have been backfilling?
could you have been backfilling?
could he have been backfilling?
could we have been backfilling?
could you have been backfilling?
could they have been backfilling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not backfill?
could you not backfill?
could he not backfill?
could we not backfill?
could you not backfill?
could they not backfill? 	could I not be backfilling?
could you not be backfilling?
could he not be backfilling?
could we not be backfilling?
could you not be backfilling?
could they not be backfilling? 	could I not have backfilled?
could you not have backfilled?
could he not have backfilled?
could we not have backfilled?
could you not have backfilled?
could they not have backfilled? 	could I not have been backfilling?
could you not have been backfilling?
could he not have been backfilling?
could we not have been backfilling?
could you not have been backfilling?
could they not have been backfilling?