must perturb
Regular verb: perturb - perturbed- perturbed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must perturb
you must perturb
he must perturb
we must perturb
you must perturb
they must perturb 	I must be perturbing
you must be perturbing
he must be perturbing
we must be perturbing
you must be perturbing
they must be perturbing	I must have perturbed
you must have perturbed
he must have perturbed
we must have perturbed
you must have perturbed
they must have perturbed	I must have been perturbing
you must have been perturbing
he must have been perturbing
we must have been perturbing
you must have been perturbing
they must have been perturbing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't perturb
you mustn't perturb
he mustn't perturb
we mustn't perturb
you mustn't perturb
they mustn't perturb 	I mustn't be perturbing
you mustn't be perturbing
he mustn't be perturbing
we mustn't be perturbing
you mustn't be perturbing
they mustn't be perturbing	I mustn't have perturbed
you mustn't have perturbed
he mustn't have perturbed
we mustn't have perturbed
you mustn't have perturbed
they mustn't have perturbed	I mustn't have been perturbing
you mustn't have been perturbing
he mustn't have been perturbing
we mustn't have been perturbing
you mustn't have been perturbing
they mustn't have been perturbing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I perturb?
must you perturb?
must he perturb?
must we perturb?
must you perturb?
must they perturb? 	must I be perturbing?
must you be perturbing?
must he be perturbing?
must we be perturbing?
must you be perturbing?
must they be perturbing? 	must I have perturbed?
must you have perturbed?
must he have perturbed?
must we have perturbed?
must you have perturbed?
must they have perturbed? 	must I have been perturbing?
must you have been perturbing?
must he have been perturbing?
must we have been perturbing?
must you have been perturbing?
must they have been perturbing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I perturb?
mustn't you perturb?
mustn't he perturb?
mustn't we perturb?
mustn't you perturb?
mustn't they perturb? 	mustn't I be perturbing?
mustn't you be perturbing?
mustn't he be perturbing?
mustn't we be perturbing?
mustn't you be perturbing?
mustn't they be perturbing? 	mustn't I have perturbed?
mustn't you have perturbed?
mustn't he have perturbed?
mustn't we have perturbed?
mustn't you have perturbed?
mustn't they have perturbed? 	mustn't I have been perturbing?
mustn't you have been perturbing?
mustn't he have been perturbing?
mustn't we have been perturbing?
mustn't you have been perturbing?
mustn't they have been perturbing?