could cluster
Regular verb: cluster - clustered- clustered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could cluster
you could cluster
he could cluster
we could cluster
you could cluster
they could cluster 	I could be clustering
you could be clustering
he could be clustering
we could be clustering
you could be clustering
they could be clustering	I could have clustered
you could have clustered
he could have clustered
we could have clustered
you could have clustered
they could have clustered	I could have been clustering
you could have been clustering
he could have been clustering
we could have been clustering
you could have been clustering
they could have been clustering	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't cluster
you couldn't cluster
he couldn't cluster
we couldn't cluster
you couldn't cluster
they couldn't cluster 	I couldn't be clustering
you couldn't be clustering
he couldn't be clustering
we couldn't be clustering
you couldn't be clustering
they couldn't be clustering	I couldn't have clustered
you couldn't have clustered
he couldn't have clustered
we couldn't have clustered
you couldn't have clustered
they couldn't have clustered	I couldn't have been clustering
you couldn't have been clustering
he couldn't have been clustering
we couldn't have been clustering
you couldn't have been clustering
they couldn't have been clustering	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I cluster?
could you cluster?
could he cluster?
could we cluster?
could you cluster?
could they cluster? 	could I be clustering?
could you be clustering?
could he be clustering?
could we be clustering?
could you be clustering?
could they be clustering? 	could I have clustered?
could you have clustered?
could he have clustered?
could we have clustered?
could you have clustered?
could they have clustered? 	could I have been clustering?
could you have been clustering?
could he have been clustering?
could we have been clustering?
could you have been clustering?
could they have been clustering? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I cluster?
couldn't you cluster?
couldn't he cluster?
couldn't we cluster?
couldn't you cluster?
couldn't they cluster? 	couldn't I be clustering?
couldn't you be clustering?
couldn't he be clustering?
couldn't we be clustering?
couldn't you be clustering?
couldn't they be clustering? 	couldn't I have clustered?
couldn't you have clustered?
couldn't he have clustered?
couldn't we have clustered?
couldn't you have clustered?
couldn't they have clustered? 	couldn't I have been clustering?
couldn't you have been clustering?
couldn't he have been clustering?
couldn't we have been clustering?
couldn't you have been clustering?
couldn't they have been clustering?