can strengthen
Regular verb: strengthen - strengthened- strengthened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I can strengthen
you can strengthen
he can strengthen
we can strengthen
you can strengthen
they can strengthen 	I can be strengthening
you can be strengthening
he can be strengthening
we can be strengthening
you can be strengthening
they can be strengthening	I can have strengthened
you can have strengthened
he 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
he 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 can't strengthen
you can't strengthen
he can't strengthen
we can't strengthen
you can't strengthen
they can't strengthen 	I can't be strengthening
you can't be strengthening
he can't be strengthening
we can't be strengthening
you can't be strengthening
they can't be strengthening	I can't have strengthened
you can't have strengthened
he can't have strengthened
we can't have strengthened
you can't have strengthened
they can't have strengthened	I can't have been strengthening
you can't have been strengthening
he can't have been strengthening
we can't have been strengthening
you can't have been strengthening
they can't have been strengthening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
can I strengthen?
can you strengthen?
can he strengthen?
can we strengthen?
can you strengthen?
can they strengthen? 	can I be strengthening?
can you be strengthening?
can he be strengthening?
can we be strengthening?
can you be strengthening?
can they be strengthening? 	can I have strengthened?
can you have strengthened?
can he 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 he 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't I strengthen?
can't you strengthen?
can't he strengthen?
can't we strengthen?
can't you strengthen?
can't they strengthen? 	can't I be strengthening?
can't you be strengthening?
can't he be strengthening?
can't we be strengthening?
can't you be strengthening?
can't they be strengthening? 	can't I have strengthened?
can't you have strengthened?
can't he have strengthened?
can't we have strengthened?
can't you have strengthened?
can't they have strengthened? 	can't I have been strengthening?
can't you have been strengthening?
can't he have been strengthening?
can't we have been strengthening?
can't you have been strengthening?
can't they have been strengthening?