can/can't(+)I can play tennis
(-)I can't speak Italian
(+)We can study together
(-)They can't cycle to work
(?)Can you see me?
(-)I can't go out, I'm tired.
(?) Can I borrow a pen?
(+)I could lend you some money
could/couldn't(+)I could walk to primary school
(?) Could you swim when you were 2?
(-) I couldn't drive when I was a child
(?) Could you open the door for me?