could obstruct
Regular verb: obstruct - obstructed- obstructed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could obstruct
you could obstruct
he could obstruct
we could obstruct
you could obstruct
they could obstruct 	I could be obstructing
you could be obstructing
he could be obstructing
we could be obstructing
you could be obstructing
they could be obstructing	I could have obstructed
you could have obstructed
he could have obstructed
we could have obstructed
you could have obstructed
they could have obstructed	I could have been obstructing
you could have been obstructing
he could have been obstructing
we could have been obstructing
you could have been obstructing
they could have been obstructing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't obstruct
you couldn't obstruct
he couldn't obstruct
we couldn't obstruct
you couldn't obstruct
they couldn't obstruct 	I couldn't be obstructing
you couldn't be obstructing
he couldn't be obstructing
we couldn't be obstructing
you couldn't be obstructing
they couldn't be obstructing	I couldn't have obstructed
you couldn't have obstructed
he couldn't have obstructed
we couldn't have obstructed
you couldn't have obstructed
they couldn't have obstructed	I couldn't have been obstructing
you couldn't have been obstructing
he couldn't have been obstructing
we couldn't have been obstructing
you couldn't have been obstructing
they couldn't have been obstructing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I obstruct?
could you obstruct?
could he obstruct?
could we obstruct?
could you obstruct?
could they obstruct? 	could I be obstructing?
could you be obstructing?
could he be obstructing?
could we be obstructing?
could you be obstructing?
could they be obstructing? 	could I have obstructed?
could you have obstructed?
could he have obstructed?
could we have obstructed?
could you have obstructed?
could they have obstructed? 	could I have been obstructing?
could you have been obstructing?
could he have been obstructing?
could we have been obstructing?
could you have been obstructing?
could they have been obstructing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I obstruct?
couldn't you obstruct?
couldn't he obstruct?
couldn't we obstruct?
couldn't you obstruct?
couldn't they obstruct? 	couldn't I be obstructing?
couldn't you be obstructing?
couldn't he be obstructing?
couldn't we be obstructing?
couldn't you be obstructing?
couldn't they be obstructing? 	couldn't I have obstructed?
couldn't you have obstructed?
couldn't he have obstructed?
couldn't we have obstructed?
couldn't you have obstructed?
couldn't they have obstructed? 	couldn't I have been obstructing?
couldn't you have been obstructing?
couldn't he have been obstructing?
couldn't we have been obstructing?
couldn't you have been obstructing?
couldn't they have been obstructing?