English verb conjugation
MUST QUACK

Regular verb: quack - quacked - quacked

Affirmation

Simple form	V-ing form
I must quack you must quack he must quack we must quack you must quack they must quack	I must be quacking you must be quacking he must be quacking we must be quacking you must be quacking they must be quacking
Perfect	V-ing perfect
I must have quacked you must have quacked he must have quacked we must have quacked you must have quacked they must have quacked	I must have been quacking you must have been quacking he must have been quacking we must have been quacking you must have been quacking they must have been quacking

Negation

Simple form	V-ing form
I mustn't quack you mustn't quack he mustn't quack we mustn't quack you mustn't quack they mustn't quack	I mustn't be quacking you mustn't be quacking he mustn't be quacking we mustn't be quacking you mustn't be quacking they mustn't be quacking
Perfect	V-ing perfect
I mustn't have quacked you mustn't have quacked he mustn't have quacked we mustn't have quacked you mustn't have quacked they mustn't have quacked	I mustn't have been quacking you mustn't have been quacking he mustn't have been quacking we mustn't have been quacking you mustn't have been quacking they mustn't have been quacking

Interrogative form

Simple form	V-ing form
must I quack? must you quack? must he quack? must we quack? must you quack? must they quack?	must I be quacking? must you be quacking? must he be quacking? must we be quacking? must you be quacking? must they be quacking?
Perfect	V-ing perfect
must I have quacked? must you have quacked? must he have quacked? must we have quacked? must you have quacked? must they have quacked?	must I have been quacking? must you have been quacking? must he have been quacking? must we have been quacking? must you have been quacking? must they have been quacking?

Interro-negative form

Simple form	V-ing form
mustn't I quack? mustn't you quack? mustn't he quack? mustn't we quack? mustn't you quack? mustn't they quack?	mustn't I be quacking? mustn't you be quacking? mustn't he be quacking? mustn't we be quacking? mustn't you be quacking? mustn't they be quacking?
Perfect	V-ing perfect
mustn't I have quacked? mustn't you have quacked? mustn't he have quacked? mustn't we have quacked? mustn't you have quacked? mustn't they have quacked?	mustn't I have been quacking? mustn't you have been quacking? mustn't he have been quacking? mustn't we have been quacking? mustn't you have been quacking? mustn't they have been quacking?