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