I can stack you can stack he can stack we can stack you can stack they can stack
V-ing form
I can be stacking you can be stacking he can be stacking we can be stacking you can be stacking they can be stacking
Perfect
I can have stacked you can have stacked he can have stacked we can have stacked you can have stacked they can have stacked
V-ing perfect
I can have been stacking you can have been stacking he can have been stacking we can have been stacking you can have been stacking they can have been stacking
Negation
Simple form
I cannot stack you cannot stack he cannot stack we cannot stack you cannot stack they cannot stack
V-ing form
I cannot be stacking you cannot be stacking he cannot be stacking we cannot be stacking you cannot be stacking they cannot be stacking
Perfect
I cannot have stacked you cannot have stacked he cannot have stacked we cannot have stacked you cannot have stacked they cannot have stacked
V-ing perfect
I cannot have been stacking you cannot have been stacking he cannot have been stacking we cannot have been stacking you cannot have been stacking they cannot have been stacking
Interrogative form
Simple form
can I stack? can you stack? can he stack? can we stack? can you stack? can they stack?
V-ing form
can I be stacking? can you be stacking? can he be stacking? can we be stacking? can you be stacking? can they be stacking?
Perfect
can I have stacked? can you have stacked? can he have stacked? can we have stacked? can you have stacked? can they have stacked?
V-ing perfect
can I have been stacking? can you have been stacking? can he have been stacking? can we have been stacking? can you have been stacking? can they have been stacking?
Interro-negative form
Simple form
can I not stack? can you not stack? can he not stack? can we not stack? can you not stack? can they not stack?
V-ing form
can I not be stacking? can you not be stacking? can he not be stacking? can we not be stacking? can you not be stacking? can they not be stacking?
Perfect
can I not have stacked? can you not have stacked? can he not have stacked? can we not have stacked? can you not have stacked? can they not have stacked?
V-ing perfect
can I not have been stacking? can you not have been stacking? can he not have been stacking? can we not have been stacking? can you not have been stacking? can they not have been stacking?