写出下列动词的过去式。
(1) work ____________ (2) study ______________ (3) look _______________
(4) live _____________ (5) plan _______________ (6) have _______________
(7) use _____________ (8) carry _______________ (9) stop _______________
(10) are _____________ (11) bring ______________ (12) buy _______________