can strengthen
Regular verb: strengthen - strengthened- strengthened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I can strengthen
you can strengthen
she can strengthen
we can strengthen
you can strengthen
they can strengthen 	I can be strengthening
you can be strengthening
she can be strengthening
we can be strengthening
you can be strengthening
they can be strengthening	I can have strengthened
you can have strengthened
she can have strengthened
we can have strengthened
you can have strengthened
they can have strengthened	I can have been strengthening
you can have been strengthening
she can have been strengthening
we can have been strengthening
you can have been strengthening
they can have been strengthening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I cannot strengthen
you cannot strengthen
she cannot strengthen
we cannot strengthen
you cannot strengthen
they cannot strengthen 	I cannot be strengthening
you cannot be strengthening
she cannot be strengthening
we cannot be strengthening
you cannot be strengthening
they cannot be strengthening	I cannot have strengthened
you cannot have strengthened
she cannot have strengthened
we cannot have strengthened
you cannot have strengthened
they cannot have strengthened	I cannot have been strengthening
you cannot have been strengthening
she cannot have been strengthening
we cannot have been strengthening
you cannot have been strengthening
they cannot have been strengthening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
can I strengthen?
can you strengthen?
can she strengthen?
can we strengthen?
can you strengthen?
can they strengthen? 	can I be strengthening?
can you be strengthening?
can she be strengthening?
can we be strengthening?
can you be strengthening?
can they be strengthening? 	can I have strengthened?
can you have strengthened?
can she have strengthened?
can we have strengthened?
can you have strengthened?
can they have strengthened? 	can I have been strengthening?
can you have been strengthening?
can she have been strengthening?
can we have been strengthening?
can you have been strengthening?
can they have been strengthening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
can I not strengthen?
can you not strengthen?
can she not strengthen?
can we not strengthen?
can you not strengthen?
can they not strengthen? 	can I not be strengthening?
can you not be strengthening?
can she not be strengthening?
can we not be strengthening?
can you not be strengthening?
can they not be strengthening? 	can I not have strengthened?
can you not have strengthened?
can she not have strengthened?
can we not have strengthened?
can you not have strengthened?
can they not have strengthened? 	can I not have been strengthening?
can you not have been strengthening?
can she not have been strengthening?
can we not have been strengthening?
can you not have been strengthening?
can they not have been strengthening?