I can lack you can lack she can lack we can lack you can lack they can lack
V-ing form
I can be lacking you can be lacking she can be lacking we can be lacking you can be lacking they can be lacking
Perfect
I can have lacked you can have lacked she can have lacked we can have lacked you can have lacked they can have lacked
V-ing perfect
I can have been lacking you can have been lacking she can have been lacking we can have been lacking you can have been lacking they can have been lacking
Negation
Simple form
I cannot lack you cannot lack she cannot lack we cannot lack you cannot lack they cannot lack
V-ing form
I cannot be lacking you cannot be lacking she cannot be lacking we cannot be lacking you cannot be lacking they cannot be lacking
Perfect
I cannot have lacked you cannot have lacked she cannot have lacked we cannot have lacked you cannot have lacked they cannot have lacked
V-ing perfect
I cannot have been lacking you cannot have been lacking she cannot have been lacking we cannot have been lacking you cannot have been lacking they cannot have been lacking
Interrogative form
Simple form
can I lack? can you lack? can she lack? can we lack? can you lack? can they lack?
V-ing form
can I be lacking? can you be lacking? can she be lacking? can we be lacking? can you be lacking? can they be lacking?
Perfect
can I have lacked? can you have lacked? can she have lacked? can we have lacked? can you have lacked? can they have lacked?
V-ing perfect
can I have been lacking? can you have been lacking? can she have been lacking? can we have been lacking? can you have been lacking? can they have been lacking?
Interro-negative form
Simple form
can I not lack? can you not lack? can she not lack? can we not lack? can you not lack? can they not lack?
V-ing form
can I not be lacking? can you not be lacking? can she not be lacking? can we not be lacking? can you not be lacking? can they not be lacking?
Perfect
can I not have lacked? can you not have lacked? can she not have lacked? can we not have lacked? can you not have lacked? can they not have lacked?
V-ing perfect
can I not have been lacking? can you not have been lacking? can she not have been lacking? can we not have been lacking? can you not have been lacking? can they not have been lacking?