can lengthen
Regular verb: lengthen - lengthened- lengthened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I can lengthen
you can lengthen
she can lengthen
we can lengthen
you can lengthen
they can lengthen 	I can be lengthening
you can be lengthening
she can be lengthening
we can be lengthening
you can be lengthening
they can be lengthening	I can have lengthened
you can have lengthened
she can have lengthened
we can have lengthened
you can have lengthened
they can have lengthened	I can have been lengthening
you can have been lengthening
she can have been lengthening
we can have been lengthening
you can have been lengthening
they can have been lengthening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I cannot lengthen
you cannot lengthen
she cannot lengthen
we cannot lengthen
you cannot lengthen
they cannot lengthen 	I cannot be lengthening
you cannot be lengthening
she cannot be lengthening
we cannot be lengthening
you cannot be lengthening
they cannot be lengthening	I cannot have lengthened
you cannot have lengthened
she cannot have lengthened
we cannot have lengthened
you cannot have lengthened
they cannot have lengthened	I cannot have been lengthening
you cannot have been lengthening
she cannot have been lengthening
we cannot have been lengthening
you cannot have been lengthening
they cannot have been lengthening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
can I lengthen?
can you lengthen?
can she lengthen?
can we lengthen?
can you lengthen?
can they lengthen? 	can I be lengthening?
can you be lengthening?
can she be lengthening?
can we be lengthening?
can you be lengthening?
can they be lengthening? 	can I have lengthened?
can you have lengthened?
can she have lengthened?
can we have lengthened?
can you have lengthened?
can they have lengthened? 	can I have been lengthening?
can you have been lengthening?
can she have been lengthening?
can we have been lengthening?
can you have been lengthening?
can they have been lengthening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
can I not lengthen?
can you not lengthen?
can she not lengthen?
can we not lengthen?
can you not lengthen?
can they not lengthen? 	can I not be lengthening?
can you not be lengthening?
can she not be lengthening?
can we not be lengthening?
can you not be lengthening?
can they not be lengthening? 	can I not have lengthened?
can you not have lengthened?
can she not have lengthened?
can we not have lengthened?
can you not have lengthened?
can they not have lengthened? 	can I not have been lengthening?
can you not have been lengthening?
can she not have been lengthening?
can we not have been lengthening?
can you not have been lengthening?
can they not have been lengthening?