I must flex you must flex he must flex we must flex you must flex they must flex
V-ing form
I must be flexing you must be flexing he must be flexing we must be flexing you must be flexing they must be flexing
Perfect
I must have flexed you must have flexed he must have flexed we must have flexed you must have flexed they must have flexed
V-ing perfect
I must have been flexing you must have been flexing he must have been flexing we must have been flexing you must have been flexing they must have been flexing
Negation
Simple form
I mustn't flex you mustn't flex he mustn't flex we mustn't flex you mustn't flex they mustn't flex
V-ing form
I mustn't be flexing you mustn't be flexing he mustn't be flexing we mustn't be flexing you mustn't be flexing they mustn't be flexing
Perfect
I mustn't have flexed you mustn't have flexed he mustn't have flexed we mustn't have flexed you mustn't have flexed they mustn't have flexed
V-ing perfect
I mustn't have been flexing you mustn't have been flexing he mustn't have been flexing we mustn't have been flexing you mustn't have been flexing they mustn't have been flexing
Interrogative form
Simple form
must I flex? must you flex? must he flex? must we flex? must you flex? must they flex?
V-ing form
must I be flexing? must you be flexing? must he be flexing? must we be flexing? must you be flexing? must they be flexing?
Perfect
must I have flexed? must you have flexed? must he have flexed? must we have flexed? must you have flexed? must they have flexed?
V-ing perfect
must I have been flexing? must you have been flexing? must he have been flexing? must we have been flexing? must you have been flexing? must they have been flexing?
Interro-negative form
Simple form
mustn't I flex? mustn't you flex? mustn't he flex? mustn't we flex? mustn't you flex? mustn't they flex?
V-ing form
mustn't I be flexing? mustn't you be flexing? mustn't he be flexing? mustn't we be flexing? mustn't you be flexing? mustn't they be flexing?
Perfect
mustn't I have flexed? mustn't you have flexed? mustn't he have flexed? mustn't we have flexed? mustn't you have flexed? mustn't they have flexed?
V-ing perfect
mustn't I have been flexing? mustn't you have been flexing? mustn't he have been flexing? mustn't we have been flexing? mustn't you have been flexing? mustn't they have been flexing?