English verb conjugation
MUST LENGTHEN

Regular verb: lengthen - lengthened - lengthened

Affirmation

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

Negation

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

Interrogative form

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

Interro-negative form

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