could stem
Verbo regular: stem - stemmed- stemmed

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could stem
you could stem
she could stem
we could stem
you could stem
they could stem 	I could be stemming
you could be stemming
she could be stemming
we could be stemming
you could be stemming
they could be stemming	I could have stemmed
you could have stemmed
she could have stemmed
we could have stemmed
you could have stemmed
they could have stemmed	I could have been stemming
you could have been stemming
she could have been stemming
we could have been stemming
you could have been stemming
they could have been stemming	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I couldn't stem
you couldn't stem
she couldn't stem
we couldn't stem
you couldn't stem
they couldn't stem 	I couldn't be stemming
you couldn't be stemming
she couldn't be stemming
we couldn't be stemming
you couldn't be stemming
they couldn't be stemming	I couldn't have stemmed
you couldn't have stemmed
she couldn't have stemmed
we couldn't have stemmed
you couldn't have stemmed
they couldn't have stemmed	I couldn't have been stemming
you couldn't have been stemming
she couldn't have been stemming
we couldn't have been stemming
you couldn't have been stemming
they couldn't have been stemming	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I stem?
could you stem?
could she stem?
could we stem?
could you stem?
could they stem? 	could I be stemming?
could you be stemming?
could she be stemming?
could we be stemming?
could you be stemming?
could they be stemming? 	could I have stemmed?
could you have stemmed?
could she have stemmed?
could we have stemmed?
could you have stemmed?
could they have stemmed? 	could I have been stemming?
could you have been stemming?
could she have been stemming?
could we have been stemming?
could you have been stemming?
could they have been stemming? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
couldn't I stem?
couldn't you stem?
couldn't she stem?
couldn't we stem?
couldn't you stem?
couldn't they stem? 	couldn't I be stemming?
couldn't you be stemming?
couldn't she be stemming?
couldn't we be stemming?
couldn't you be stemming?
couldn't they be stemming? 	couldn't I have stemmed?
couldn't you have stemmed?
couldn't she have stemmed?
couldn't we have stemmed?
couldn't you have stemmed?
couldn't they have stemmed? 	couldn't I have been stemming?
couldn't you have been stemming?
couldn't she have been stemming?
couldn't we have been stemming?
couldn't you have been stemming?
couldn't they have been stemming?