I could sell you could sell he could sell we could sell you could sell they could sell
V-ing form
I could be selling you could be selling he could be selling we could be selling you could be selling they could be selling
Perfect
I could have sold you could have sold he could have sold we could have sold you could have sold they could have sold
V-ing perfect
I could have been selling you could have been selling he could have been selling we could have been selling you could have been selling they could have been selling
Negation
Simple form
I couldn't sell you couldn't sell he couldn't sell we couldn't sell you couldn't sell they couldn't sell
V-ing form
I couldn't be selling you couldn't be selling he couldn't be selling we couldn't be selling you couldn't be selling they couldn't be selling
Perfect
I couldn't have sold you couldn't have sold he couldn't have sold we couldn't have sold you couldn't have sold they couldn't have sold
V-ing perfect
I couldn't have been selling you couldn't have been selling he couldn't have been selling we couldn't have been selling you couldn't have been selling they couldn't have been selling
Interrogative form
Simple form
could I sell? could you sell? could he sell? could we sell? could you sell? could they sell?
V-ing form
could I be selling? could you be selling? could he be selling? could we be selling? could you be selling? could they be selling?
Perfect
could I have sold? could you have sold? could he have sold? could we have sold? could you have sold? could they have sold?
V-ing perfect
could I have been selling? could you have been selling? could he have been selling? could we have been selling? could you have been selling? could they have been selling?
Interro-negative form
Simple form
couldn't I sell? couldn't you sell? couldn't he sell? couldn't we sell? couldn't you sell? couldn't they sell?
V-ing form
couldn't I be selling? couldn't you be selling? couldn't he be selling? couldn't we be selling? couldn't you be selling? couldn't they be selling?
Perfect
couldn't I have sold? couldn't you have sold? couldn't he have sold? couldn't we have sold? couldn't you have sold? couldn't they have sold?
V-ing perfect
couldn't I have been selling? couldn't you have been selling? couldn't he have been selling? couldn't we have been selling? couldn't you have been selling? couldn't they have been selling?