I can sell you can sell she can sell we can sell you can sell they can sell
V-ing form
I can be selling you can be selling she can be selling we can be selling you can be selling they can be selling
Perfect
I can have sold you can have sold she can have sold we can have sold you can have sold they can have sold
V-ing perfect
I can have been selling you can have been selling she can have been selling we can have been selling you can have been selling they can have been selling
Negation
Simple form
I cannot sell you cannot sell she cannot sell we cannot sell you cannot sell they cannot sell
V-ing form
I cannot be selling you cannot be selling she cannot be selling we cannot be selling you cannot be selling they cannot be selling
Perfect
I cannot have sold you cannot have sold she cannot have sold we cannot have sold you cannot have sold they cannot have sold
V-ing perfect
I cannot have been selling you cannot have been selling she cannot have been selling we cannot have been selling you cannot have been selling they cannot have been selling
Interrogative form
Simple form
can I sell? can you sell? can she sell? can we sell? can you sell? can they sell?
V-ing form
can I be selling? can you be selling? can she be selling? can we be selling? can you be selling? can they be selling?
Perfect
can I have sold? can you have sold? can she have sold? can we have sold? can you have sold? can they have sold?
V-ing perfect
can I have been selling? can you have been selling? can she have been selling? can we have been selling? can you have been selling? can they have been selling?
Interro-negative form
Simple form
can I not sell? can you not sell? can she not sell? can we not sell? can you not sell? can they not sell?
V-ing form
can I not be selling? can you not be selling? can she not be selling? can we not be selling? can you not be selling? can they not be selling?
Perfect
can I not have sold? can you not have sold? can she not have sold? can we not have sold? can you not have sold? can they not have sold?
V-ing perfect
can I not have been selling? can you not have been selling? can she not have been selling? can we not have been selling? can you not have been selling? can they not have been selling?