Основное правило:
Can - в настоящее время.
Could - в прошедшем.
Ответ:
(1) I CAN drive bus now, but I COULDN'T when I was sixteen.
(2) He COULDN'T go out last night.
(3) How COULD I have been so silly when I was a teenager.
(4) Birds and bats CAN fly.
(5) We did the best we COULD.
(6) In 1870 we COULDN'T listen to the radio, but now we CAN.
(7) I CAN'T play golf tomorrow.
(8) There was nothing we COULD do for you.
-------------------------------------------------------------------------------------------