could mask
Regular verb: mask - masked- masked

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

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

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

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