could challenge
Regular verb: challenge - challenged- challenged

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could challenge
you could challenge
she could challenge
we could challenge
you could challenge
they could challenge 	I could be challenging
you could be challenging
she could be challenging
we could be challenging
you could be challenging
they could be challenging	I could have challenged
you could have challenged
she 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
she 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 could not challenge
you could not challenge
she could not challenge
we could not challenge
you could not challenge
they could not challenge 	I could not be challenging
you could not be challenging
she could not be challenging
we could not be challenging
you could not be challenging
they could not be challenging	I could not have challenged
you could not have challenged
she could not have challenged
we could not have challenged
you could not have challenged
they could not have challenged	I could not have been challenging
you could not have been challenging
she could not have been challenging
we could not have been challenging
you could not have been challenging
they could not have been challenging	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I challenge?
could you challenge?
could she challenge?
could we challenge?
could you challenge?
could they challenge? 	could I be challenging?
could you be challenging?
could she be challenging?
could we be challenging?
could you be challenging?
could they be challenging? 	could I have challenged?
could you have challenged?
could she 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 she 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 	
could I not challenge?
could you not challenge?
could she not challenge?
could we not challenge?
could you not challenge?
could they not challenge? 	could I not be challenging?
could you not be challenging?
could she not be challenging?
could we not be challenging?
could you not be challenging?
could they not be challenging? 	could I not have challenged?
could you not have challenged?
could she not have challenged?
could we not have challenged?
could you not have challenged?
could they not have challenged? 	could I not have been challenging?
could you not have been challenging?
could she not have been challenging?
could we not have been challenging?
could you not have been challenging?
could they not have been challenging?