I can challenge you can challenge she can challenge we can challenge you can challenge they can challenge
V-ing form
I can be challenging you can be challenging she can be challenging we can be challenging you can be challenging they can be challenging
Perfect
I can have challenged you can have challenged she can have challenged we can have challenged you can have challenged they can have challenged
V-ing perfect
I can have been challenging you can have been challenging she can have been challenging we can have been challenging you can have been challenging they can have been challenging
Negation
Simple form
I can't challenge you can't challenge she can't challenge we can't challenge you can't challenge they can't challenge
V-ing form
I can't be challenging you can't be challenging she can't be challenging we can't be challenging you can't be challenging they can't be challenging
Perfect
I can't have challenged you can't have challenged she can't have challenged we can't have challenged you can't have challenged they can't have challenged
V-ing perfect
I can't have been challenging you can't have been challenging she can't have been challenging we can't have been challenging you can't have been challenging they can't have been challenging
Interrogative form
Simple form
can I challenge? can you challenge? can she challenge? can we challenge? can you challenge? can they challenge?
V-ing form
can I be challenging? can you be challenging? can she be challenging? can we be challenging? can you be challenging? can they be challenging?
Perfect
can I have challenged? can you have challenged? can she have challenged? can we have challenged? can you have challenged? can they have challenged?
V-ing perfect
can I have been challenging? can you have been challenging? can she have been challenging? can we have been challenging? can you have been challenging? can they have been challenging?
Interro-negative form
Simple form
can't I challenge? can't you challenge? can't she challenge? can't we challenge? can't you challenge? can't they challenge?
V-ing form
can't I be challenging? can't you be challenging? can't she be challenging? can't we be challenging? can't you be challenging? can't they be challenging?
Perfect
can't I have challenged? can't you have challenged? can't she have challenged? can't we have challenged? can't you have challenged? can't they have challenged?
V-ing perfect
can't I have been challenging? can't you have been challenging? can't she have been challenging? can't we have been challenging? can't you have been challenging? can't they have been challenging?