I could register you could register she could register we could register you could register they could register
V-ing form
I could be registering you could be registering she could be registering we could be registering you could be registering they could be registering
Perfect
I could have registered you could have registered she could have registered we could have registered you could have registered they could have registered
V-ing perfect
I could have been registering you could have been registering she could have been registering we could have been registering you could have been registering they could have been registering
Negation
Simple form
I could not register you could not register she could not register we could not register you could not register they could not register
V-ing form
I could not be registering you could not be registering she could not be registering we could not be registering you could not be registering they could not be registering
Perfect
I could not have registered you could not have registered she could not have registered we could not have registered you could not have registered they could not have registered
V-ing perfect
I could not have been registering you could not have been registering she could not have been registering we could not have been registering you could not have been registering they could not have been registering
Interrogative form
Simple form
could I register? could you register? could she register? could we register? could you register? could they register?
V-ing form
could I be registering? could you be registering? could she be registering? could we be registering? could you be registering? could they be registering?
Perfect
could I have registered? could you have registered? could she have registered? could we have registered? could you have registered? could they have registered?
V-ing perfect
could I have been registering? could you have been registering? could she have been registering? could we have been registering? could you have been registering? could they have been registering?
Interro-negative form
Simple form
could I not register? could you not register? could she not register? could we not register? could you not register? could they not register?
V-ing form
could I not be registering? could you not be registering? could she not be registering? could we not be registering? could you not be registering? could they not be registering?
Perfect
could I not have registered? could you not have registered? could she not have registered? could we not have registered? could you not have registered? could they not have registered?
V-ing perfect
could I not have been registering? could you not have been registering? could she not have been registering? could we not have been registering? could you not have been registering? could they not have been registering?