must mask
Regular verb: mask - masked- masked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must mask
you must mask
he must mask
we must mask
you must mask
they must mask 	I must be masking
you must be masking
he must be masking
we must be masking
you must be masking
they must be masking	I must have masked
you must have masked
he must have masked
we must have masked
you must have masked
they must have masked	I must have been masking
you must have been masking
he must have been masking
we must have been masking
you must have been masking
they must have been masking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't mask
you mustn't mask
he mustn't mask
we mustn't mask
you mustn't mask
they mustn't mask 	I mustn't be masking
you mustn't be masking
he mustn't be masking
we mustn't be masking
you mustn't be masking
they mustn't be masking	I mustn't have masked
you mustn't have masked
he mustn't have masked
we mustn't have masked
you mustn't have masked
they mustn't have masked	I mustn't have been masking
you mustn't have been masking
he mustn't have been masking
we mustn't have been masking
you mustn't have been masking
they mustn't have been masking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I mask?
must you mask?
must he mask?
must we mask?
must you mask?
must they mask? 	must I be masking?
must you be masking?
must he be masking?
must we be masking?
must you be masking?
must they be masking? 	must I have masked?
must you have masked?
must he have masked?
must we have masked?
must you have masked?
must they have masked? 	must I have been masking?
must you have been masking?
must he have been masking?
must we have been masking?
must you have been masking?
must they have been masking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I mask?
mustn't you mask?
mustn't he mask?
mustn't we mask?
mustn't you mask?
mustn't they mask? 	mustn't I be masking?
mustn't you be masking?
mustn't he be masking?
mustn't we be masking?
mustn't you be masking?
mustn't they be masking? 	mustn't I have masked?
mustn't you have masked?
mustn't he have masked?
mustn't we have masked?
mustn't you have masked?
mustn't they have masked? 	mustn't I have been masking?
mustn't you have been masking?
mustn't he have been masking?
mustn't we have been masking?
mustn't you have been masking?
mustn't they have been masking?