could challenge
Regular verb: challenge - challenged- challenged

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could challenge
you could challenge
he could challenge
we could challenge
you could challenge
they could challenge 	I could be challenging
you could be challenging
he could be challenging
we could be challenging
you could be challenging
they could be challenging	I could have challenged
you could have challenged
he could have challenged
we could have challenged
you could have challenged
they could have challenged	I could have been challenging
you could have been challenging
he could have been challenging
we could have been challenging
you could have been challenging
they could have been challenging	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't challenge
you couldn't challenge
he couldn't challenge
we couldn't challenge
you couldn't challenge
they couldn't challenge 	I couldn't be challenging
you couldn't be challenging
he couldn't be challenging
we couldn't be challenging
you couldn't be challenging
they couldn't be challenging	I couldn't have challenged
you couldn't have challenged
he couldn't have challenged
we couldn't have challenged
you couldn't have challenged
they couldn't have challenged	I couldn't have been challenging
you couldn't have been challenging
he couldn't have been challenging
we couldn't have been challenging
you couldn't have been challenging
they couldn't have been challenging	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I challenge?
could you challenge?
could he challenge?
could we challenge?
could you challenge?
could they challenge? 	could I be challenging?
could you be challenging?
could he be challenging?
could we be challenging?
could you be challenging?
could they be challenging? 	could I have challenged?
could you have challenged?
could he have challenged?
could we have challenged?
could you have challenged?
could they have challenged? 	could I have been challenging?
could you have been challenging?
could he have been challenging?
could we have been challenging?
could you have been challenging?
could they have been challenging? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I challenge?
couldn't you challenge?
couldn't he challenge?
couldn't we challenge?
couldn't you challenge?
couldn't they challenge? 	couldn't I be challenging?
couldn't you be challenging?
couldn't he be challenging?
couldn't we be challenging?
couldn't you be challenging?
couldn't they be challenging? 	couldn't I have challenged?
couldn't you have challenged?
couldn't he have challenged?
couldn't we have challenged?
couldn't you have challenged?
couldn't they have challenged? 	couldn't I have been challenging?
couldn't you have been challenging?
couldn't he have been challenging?
couldn't we have been challenging?
couldn't you have been challenging?
couldn't they have been challenging?