I must concentrate you must concentrate she must concentrate we must concentrate you must concentrate they must concentrate
V-ing form
I must be concentrating you must be concentrating she must be concentrating we must be concentrating you must be concentrating they must be concentrating
Perfect
I must have concentrated you must have concentrated she must have concentrated we must have concentrated you must have concentrated they must have concentrated
V-ing perfect
I must have been concentrating you must have been concentrating she must have been concentrating we must have been concentrating you must have been concentrating they must have been concentrating
Negation
Simple form
I mustn't concentrate you mustn't concentrate she mustn't concentrate we mustn't concentrate you mustn't concentrate they mustn't concentrate
V-ing form
I mustn't be concentrating you mustn't be concentrating she mustn't be concentrating we mustn't be concentrating you mustn't be concentrating they mustn't be concentrating
Perfect
I mustn't have concentrated you mustn't have concentrated she mustn't have concentrated we mustn't have concentrated you mustn't have concentrated they mustn't have concentrated
V-ing perfect
I mustn't have been concentrating you mustn't have been concentrating she mustn't have been concentrating we mustn't have been concentrating you mustn't have been concentrating they mustn't have been concentrating
Interrogative form
Simple form
must I concentrate? must you concentrate? must she concentrate? must we concentrate? must you concentrate? must they concentrate?
V-ing form
must I be concentrating? must you be concentrating? must she be concentrating? must we be concentrating? must you be concentrating? must they be concentrating?
Perfect
must I have concentrated? must you have concentrated? must she have concentrated? must we have concentrated? must you have concentrated? must they have concentrated?
V-ing perfect
must I have been concentrating? must you have been concentrating? must she have been concentrating? must we have been concentrating? must you have been concentrating? must they have been concentrating?
Interro-negative form
Simple form
mustn't I concentrate? mustn't you concentrate? mustn't she concentrate? mustn't we concentrate? mustn't you concentrate? mustn't they concentrate?
V-ing form
mustn't I be concentrating? mustn't you be concentrating? mustn't she be concentrating? mustn't we be concentrating? mustn't you be concentrating? mustn't they be concentrating?
Perfect
mustn't I have concentrated? mustn't you have concentrated? mustn't she have concentrated? mustn't we have concentrated? mustn't you have concentrated? mustn't they have concentrated?
V-ing perfect
mustn't I have been concentrating? mustn't you have been concentrating? mustn't she have been concentrating? mustn't we have been concentrating? mustn't you have been concentrating? mustn't they have been concentrating?