I could yelp you could yelp he could yelp we could yelp you could yelp they could yelp
V-ing form
I could be yelping you could be yelping he could be yelping we could be yelping you could be yelping they could be yelping
Perfect
I could have yelped you could have yelped he could have yelped we could have yelped you could have yelped they could have yelped
V-ing perfect
I could have been yelping you could have been yelping he could have been yelping we could have been yelping you could have been yelping they could have been yelping
Negation
Simple form
I couldn't yelp you couldn't yelp he couldn't yelp we couldn't yelp you couldn't yelp they couldn't yelp
V-ing form
I couldn't be yelping you couldn't be yelping he couldn't be yelping we couldn't be yelping you couldn't be yelping they couldn't be yelping
Perfect
I couldn't have yelped you couldn't have yelped he couldn't have yelped we couldn't have yelped you couldn't have yelped they couldn't have yelped
V-ing perfect
I couldn't have been yelping you couldn't have been yelping he couldn't have been yelping we couldn't have been yelping you couldn't have been yelping they couldn't have been yelping
Interrogative form
Simple form
could I yelp? could you yelp? could he yelp? could we yelp? could you yelp? could they yelp?
V-ing form
could I be yelping? could you be yelping? could he be yelping? could we be yelping? could you be yelping? could they be yelping?
Perfect
could I have yelped? could you have yelped? could he have yelped? could we have yelped? could you have yelped? could they have yelped?
V-ing perfect
could I have been yelping? could you have been yelping? could he have been yelping? could we have been yelping? could you have been yelping? could they have been yelping?
Interro-negative form
Simple form
couldn't I yelp? couldn't you yelp? couldn't he yelp? couldn't we yelp? couldn't you yelp? couldn't they yelp?
V-ing form
couldn't I be yelping? couldn't you be yelping? couldn't he be yelping? couldn't we be yelping? couldn't you be yelping? couldn't they be yelping?
Perfect
couldn't I have yelped? couldn't you have yelped? couldn't he have yelped? couldn't we have yelped? couldn't you have yelped? couldn't they have yelped?
V-ing perfect
couldn't I have been yelping? couldn't you have been yelping? couldn't he have been yelping? couldn't we have been yelping? couldn't you have been yelping? couldn't they have been yelping?