could backfill
Regular verb: backfill - backfilled- backfilled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't backfill
you couldn't backfill
he couldn't backfill
we couldn't backfill
you couldn't backfill
they couldn't backfill 	I couldn't be backfilling
you couldn't be backfilling
he couldn't be backfilling
we couldn't be backfilling
you couldn't be backfilling
they couldn't be backfilling	I couldn't have backfilled
you couldn't have backfilled
he couldn't have backfilled
we couldn't have backfilled
you couldn't have backfilled
they couldn't have backfilled	I couldn't have been backfilling
you couldn't have been backfilling
he couldn't have been backfilling
we couldn't have been backfilling
you couldn't have been backfilling
they couldn't 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 	
couldn't I backfill?
couldn't you backfill?
couldn't he backfill?
couldn't we backfill?
couldn't you backfill?
couldn't they backfill? 	couldn't I be backfilling?
couldn't you be backfilling?
couldn't he be backfilling?
couldn't we be backfilling?
couldn't you be backfilling?
couldn't they be backfilling? 	couldn't I have backfilled?
couldn't you have backfilled?
couldn't he have backfilled?
couldn't we have backfilled?
couldn't you have backfilled?
couldn't they have backfilled? 	couldn't I have been backfilling?
couldn't you have been backfilling?
couldn't he have been backfilling?
couldn't we have been backfilling?
couldn't you have been backfilling?
couldn't they have been backfilling?