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