stay - stays - staying -stayed
spend - spends- spending - spent
sit - sits - sitting - sat
see - sees -seeing -saw
say - says - saying- said
write - writes - writing - wrote
cry- cries - crying - cried
study- studies - studying -studied
stop - stops -stopping -stopped
practice - practices - practicing - practiced
动词第三人称单数一般在词尾+s
现在分词一般在动词词尾+ing
规则动词的过去式一般在词尾+ed