could understudy
Regular verb: understudy - understudied- understudied

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could understudy
you could understudy
she could understudy
we could understudy
you could understudy
they could understudy 	I could be understudying
you could be understudying
she could be understudying
we could be understudying
you could be understudying
they could be understudying	I could have understudied
you could have understudied
she could have understudied
we could have understudied
you could have understudied
they could have understudied	I could have been understudying
you could have been understudying
she could have been understudying
we could have been understudying
you could have been understudying
they could have been understudying	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't understudy
you couldn't understudy
she couldn't understudy
we couldn't understudy
you couldn't understudy
they couldn't understudy 	I couldn't be understudying
you couldn't be understudying
she couldn't be understudying
we couldn't be understudying
you couldn't be understudying
they couldn't be understudying	I couldn't have understudied
you couldn't have understudied
she couldn't have understudied
we couldn't have understudied
you couldn't have understudied
they couldn't have understudied	I couldn't have been understudying
you couldn't have been understudying
she couldn't have been understudying
we couldn't have been understudying
you couldn't have been understudying
they couldn't have been understudying	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I understudy?
could you understudy?
could she understudy?
could we understudy?
could you understudy?
could they understudy? 	could I be understudying?
could you be understudying?
could she be understudying?
could we be understudying?
could you be understudying?
could they be understudying? 	could I have understudied?
could you have understudied?
could she have understudied?
could we have understudied?
could you have understudied?
could they have understudied? 	could I have been understudying?
could you have been understudying?
could she have been understudying?
could we have been understudying?
could you have been understudying?
could they have been understudying? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I understudy?
couldn't you understudy?
couldn't she understudy?
couldn't we understudy?
couldn't you understudy?
couldn't they understudy? 	couldn't I be understudying?
couldn't you be understudying?
couldn't she be understudying?
couldn't we be understudying?
couldn't you be understudying?
couldn't they be understudying? 	couldn't I have understudied?
couldn't you have understudied?
couldn't she have understudied?
couldn't we have understudied?
couldn't you have understudied?
couldn't they have understudied? 	couldn't I have been understudying?
couldn't you have been understudying?
couldn't she have been understudying?
couldn't we have been understudying?
couldn't you have been understudying?
couldn't they have been understudying?