must lack
Regular verb: lack - lacked- lacked

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must lack
you must lack
she must lack
we must lack
you must lack
they must lack 	I must be lacking
you must be lacking
she must be lacking
we must be lacking
you must be lacking
they must be lacking	I must have lacked
you must have lacked
she must have lacked
we must have lacked
you must have lacked
they must have lacked	I must have been lacking
you must have been lacking
she must have been lacking
we must have been lacking
you must have been lacking
they must have been lacking	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I mustn't lack
you mustn't lack
she mustn't lack
we mustn't lack
you mustn't lack
they mustn't lack 	I mustn't be lacking
you mustn't be lacking
she mustn't be lacking
we mustn't be lacking
you mustn't be lacking
they mustn't be lacking	I mustn't have lacked
you mustn't have lacked
she mustn't have lacked
we mustn't have lacked
you mustn't have lacked
they mustn't have lacked	I mustn't have been lacking
you mustn't have been lacking
she mustn't have been lacking
we mustn't have been lacking
you mustn't have been lacking
they mustn't have been lacking	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
must I lack?
must you lack?
must she lack?
must we lack?
must you lack?
must they lack? 	must I be lacking?
must you be lacking?
must she be lacking?
must we be lacking?
must you be lacking?
must they be lacking? 	must I have lacked?
must you have lacked?
must she have lacked?
must we have lacked?
must you have lacked?
must they have lacked? 	must I have been lacking?
must you have been lacking?
must she have been lacking?
must we have been lacking?
must you have been lacking?
must they have been lacking? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
mustn't I lack?
mustn't you lack?
mustn't she lack?
mustn't we lack?
mustn't you lack?
mustn't they lack? 	mustn't I be lacking?
mustn't you be lacking?
mustn't she be lacking?
mustn't we be lacking?
mustn't you be lacking?
mustn't they be lacking? 	mustn't I have lacked?
mustn't you have lacked?
mustn't she have lacked?
mustn't we have lacked?
mustn't you have lacked?
mustn't they have lacked? 	mustn't I have been lacking?
mustn't you have been lacking?
mustn't she have been lacking?
mustn't we have been lacking?
mustn't you have been lacking?
mustn't they have been lacking?