单词什么时候双写加ed

表示一般过去式的动词通常用动词的过去式形式来表示,而动词的过去式是在动词原形的基础上变化的.动词的过去式可分为规则动词和不规则动词.规则动词的过去式变化如下：
（1）一般情况下,动词词尾加 -ed ,如：worked played wanted acted
（2）以不发音的 -e 结尾动词,动词词尾加 -d,如：lived moved decided declined hoped judged raised wiped
（3）以辅音字母 + y结尾的动词,把-y变为-i 再加-ed,如：studied tried copied justified cried carried embodied emptied
（4）以一个辅音字母结尾的重读闭音节动词,双写词尾辅音字母,再加 -ed,如：stopped begged fretted dragged dropped planned dotted dripped
（5）注：不规则动词的过去式变化规律性不强,须多加记忆.go - went,make - made,get - got ,buy - bought ,come - came ,fly-flew ,is/am-was,are-were ,see-saw ,bring-brought,do-did,teach-taught,think-thought,say-said,sit-sat.read-read,spend-spent,eat-ate,give-gave,sit-sat,tell-told,write-wrote,fell-felt,find-found,hear-heard,know-knew,put-put,grow-grew,take－took,catch-caught,come-came,become-became,swim-swam,sweep—swept,sing—sang,draw—drew,