fly
study

flied
studied

以重读闭音节结尾，且末尾只有一个辅音字母

双写词尾+ed

stop
plan

stopped
planned 

不规则变化的动词过去式：
have---had are---were get---got say---said feel---felt do/does---did is---was go---went   drink--drank eat--ate bring----brought think----thought
buy----bought catch---- caught teach ---- taught sit----sat wear----wore cut----cut sweep----swept sleep——slept become----became