am/is-was
are-were
go-went
buy-bought
do-did
say-said
cut-cut
can-could
fly-flew
give-gave
get-got
know-knew
have/has-had这些我都知道啊，可是see-saw可以组成单词：跷跷板，这些有他们单独的意思么？那个，对不起，我没看懂你的问题