could sustain
Regular verb: sustain - sustained- sustained

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could sustain
you could sustain
he could sustain
we could sustain
you could sustain
they could sustain 	I could be sustaining
you could be sustaining
he could be sustaining
we could be sustaining
you could be sustaining
they could be sustaining	I could have sustained
you could have sustained
he could have sustained
we could have sustained
you could have sustained
they could have sustained	I could have been sustaining
you could have been sustaining
he could have been sustaining
we could have been sustaining
you could have been sustaining
they could have been sustaining	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not sustain
you could not sustain
he could not sustain
we could not sustain
you could not sustain
they could not sustain 	I could not be sustaining
you could not be sustaining
he could not be sustaining
we could not be sustaining
you could not be sustaining
they could not be sustaining	I could not have sustained
you could not have sustained
he could not have sustained
we could not have sustained
you could not have sustained
they could not have sustained	I could not have been sustaining
you could not have been sustaining
he could not have been sustaining
we could not have been sustaining
you could not have been sustaining
they could not have been sustaining	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I sustain?
could you sustain?
could he sustain?
could we sustain?
could you sustain?
could they sustain? 	could I be sustaining?
could you be sustaining?
could he be sustaining?
could we be sustaining?
could you be sustaining?
could they be sustaining? 	could I have sustained?
could you have sustained?
could he have sustained?
could we have sustained?
could you have sustained?
could they have sustained? 	could I have been sustaining?
could you have been sustaining?
could he have been sustaining?
could we have been sustaining?
could you have been sustaining?
could they have been sustaining? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not sustain?
could you not sustain?
could he not sustain?
could we not sustain?
could you not sustain?
could they not sustain? 	could I not be sustaining?
could you not be sustaining?
could he not be sustaining?
could we not be sustaining?
could you not be sustaining?
could they not be sustaining? 	could I not have sustained?
could you not have sustained?
could he not have sustained?
could we not have sustained?
could you not have sustained?
could they not have sustained? 	could I not have been sustaining?
could you not have been sustaining?
could he not have been sustaining?
could we not have been sustaining?
could you not have been sustaining?
could they not have been sustaining?