can mask
Regular verb: mask - masked- masked

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

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

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

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