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