could quintuple
Regular verb: quintuple - quintupled- quintupled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could quintuple
you could quintuple
he could quintuple
we could quintuple
you could quintuple
they could quintuple 	I could be quintupling
you could be quintupling
he could be quintupling
we could be quintupling
you could be quintupling
they could be quintupling	I could have quintupled
you could have quintupled
he could have quintupled
we could have quintupled
you could have quintupled
they could have quintupled	I could have been quintupling
you could have been quintupling
he could have been quintupling
we could have been quintupling
you could have been quintupling
they could have been quintupling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't quintuple
you couldn't quintuple
he couldn't quintuple
we couldn't quintuple
you couldn't quintuple
they couldn't quintuple 	I couldn't be quintupling
you couldn't be quintupling
he couldn't be quintupling
we couldn't be quintupling
you couldn't be quintupling
they couldn't be quintupling	I couldn't have quintupled
you couldn't have quintupled
he couldn't have quintupled
we couldn't have quintupled
you couldn't have quintupled
they couldn't have quintupled	I couldn't have been quintupling
you couldn't have been quintupling
he couldn't have been quintupling
we couldn't have been quintupling
you couldn't have been quintupling
they couldn't have been quintupling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I quintuple?
could you quintuple?
could he quintuple?
could we quintuple?
could you quintuple?
could they quintuple? 	could I be quintupling?
could you be quintupling?
could he be quintupling?
could we be quintupling?
could you be quintupling?
could they be quintupling? 	could I have quintupled?
could you have quintupled?
could he have quintupled?
could we have quintupled?
could you have quintupled?
could they have quintupled? 	could I have been quintupling?
could you have been quintupling?
could he have been quintupling?
could we have been quintupling?
could you have been quintupling?
could they have been quintupling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I quintuple?
couldn't you quintuple?
couldn't he quintuple?
couldn't we quintuple?
couldn't you quintuple?
couldn't they quintuple? 	couldn't I be quintupling?
couldn't you be quintupling?
couldn't he be quintupling?
couldn't we be quintupling?
couldn't you be quintupling?
couldn't they be quintupling? 	couldn't I have quintupled?
couldn't you have quintupled?
couldn't he have quintupled?
couldn't we have quintupled?
couldn't you have quintupled?
couldn't they have quintupled? 	couldn't I have been quintupling?
couldn't you have been quintupling?
couldn't he have been quintupling?
couldn't we have been quintupling?
couldn't you have been quintupling?
couldn't they have been quintupling?