could zero
Regular verb: zero - zeroed- zeroed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could zero
you could zero
he could zero
we could zero
you could zero
they could zero 	I could be zeroing
you could be zeroing
he could be zeroing
we could be zeroing
you could be zeroing
they could be zeroing	I could have zeroed
you could have zeroed
he could have zeroed
we could have zeroed
you could have zeroed
they could have zeroed	I could have been zeroing
you could have been zeroing
he could have been zeroing
we could have been zeroing
you could have been zeroing
they could have been zeroing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not zero
you could not zero
he could not zero
we could not zero
you could not zero
they could not zero 	I could not be zeroing
you could not be zeroing
he could not be zeroing
we could not be zeroing
you could not be zeroing
they could not be zeroing	I could not have zeroed
you could not have zeroed
he could not have zeroed
we could not have zeroed
you could not have zeroed
they could not have zeroed	I could not have been zeroing
you could not have been zeroing
he could not have been zeroing
we could not have been zeroing
you could not have been zeroing
they could not have been zeroing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I zero?
could you zero?
could he zero?
could we zero?
could you zero?
could they zero? 	could I be zeroing?
could you be zeroing?
could he be zeroing?
could we be zeroing?
could you be zeroing?
could they be zeroing? 	could I have zeroed?
could you have zeroed?
could he have zeroed?
could we have zeroed?
could you have zeroed?
could they have zeroed? 	could I have been zeroing?
could you have been zeroing?
could he have been zeroing?
could we have been zeroing?
could you have been zeroing?
could they have been zeroing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not zero?
could you not zero?
could he not zero?
could we not zero?
could you not zero?
could they not zero? 	could I not be zeroing?
could you not be zeroing?
could he not be zeroing?
could we not be zeroing?
could you not be zeroing?
could they not be zeroing? 	could I not have zeroed?
could you not have zeroed?
could he not have zeroed?
could we not have zeroed?
could you not have zeroed?
could they not have zeroed? 	could I not have been zeroing?
could you not have been zeroing?
could he not have been zeroing?
could we not have been zeroing?
could you not have been zeroing?
could they not have been zeroing?