could strengthen
Verbo regular: strengthen - strengthened- strengthened

Afirmação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
I could strengthen
you could strengthen
he could strengthen
we could strengthen
you could strengthen
they could strengthen 	I could be strengthening
you could be strengthening
he could be strengthening
we could be strengthening
you could be strengthening
they could be strengthening	I could have strengthened
you could have strengthened
he could have strengthened
we could have strengthened
you could have strengthened
they could have strengthened	I could have been strengthening
you could have been strengthening
he could have been strengthening
we could have been strengthening
you could have been strengthening
they could have been strengthening	

Negação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
I could not strengthen
you could not strengthen
he could not strengthen
we could not strengthen
you could not strengthen
they could not strengthen 	I could not be strengthening
you could not be strengthening
he could not be strengthening
we could not be strengthening
you could not be strengthening
they could not be strengthening	I could not have strengthened
you could not have strengthened
he could not have strengthened
we could not have strengthened
you could not have strengthened
they could not have strengthened	I could not have been strengthening
you could not have been strengthening
he could not have been strengthening
we could not have been strengthening
you could not have been strengthening
they could not have been strengthening	

Forma interrogativa 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
could I strengthen?
could you strengthen?
could he strengthen?
could we strengthen?
could you strengthen?
could they strengthen? 	could I be strengthening?
could you be strengthening?
could he be strengthening?
could we be strengthening?
could you be strengthening?
could they be strengthening? 	could I have strengthened?
could you have strengthened?
could he have strengthened?
could we have strengthened?
could you have strengthened?
could they have strengthened? 	could I have been strengthening?
could you have been strengthening?
could he have been strengthening?
could we have been strengthening?
could you have been strengthening?
could they have been strengthening? 	

Forma interro-Negação 	
Forma simple 	Forma com V-ing 	Perfeito 	Perfeito com V-ing 	
could I not strengthen?
could you not strengthen?
could he not strengthen?
could we not strengthen?
could you not strengthen?
could they not strengthen? 	could I not be strengthening?
could you not be strengthening?
could he not be strengthening?
could we not be strengthening?
could you not be strengthening?
could they not be strengthening? 	could I not have strengthened?
could you not have strengthened?
could he not have strengthened?
could we not have strengthened?
could you not have strengthened?
could they not have strengthened? 	could I not have been strengthening?
could you not have been strengthening?
could he not have been strengthening?
could we not have been strengthening?
could you not have been strengthening?
could they not have been strengthening?