walked
动词过去式变化规则：
1．一般在动词末尾加-ed,如：pull-pulled,cook-cooked
2．结尾是e加d,如：taste-tasted
3．末尾只有一个元音字母和一个辅音字母的重读闭音节,应双写末尾的辅音字母,再加-ed,如：stop-stopped
4．以“辅音字母+y”结尾的,变y为i,再加-ed,如：study-studied
5．不规则动词过去式：
am,is-was,are-were,do-did,see-saw,say-said,give-gave,get-got,go-went,come-came,have-had,eat-ate,take-took,run-ran,sing-sang,put-put,make-made,read-read,write-wrote,draw-drew,drink-drank,fly-flew,ride-rode,speak-spoke,sweep-swept,swim-swam,sit-sat ...