例如:am\is-was   are-were   have\has-had   do\does-did   can-coud   will-wouid   shall-should  swim-swam  sing-sang ring-rang sit-sat come-came give-gave run-ran drink-drank become-became begin-began buy-bought bring-brought catch-caught think-thought teach-taught send-sent build-built go-went spend-spent lose-lost lend-lent mean-menat sweep-swept feel-felt learn-learnt\smell-smel sleep=slept