怎样的单词要双写末字母再加ing?

1、以重读闭音节结尾,末尾只有一个辅音字母的动词,要双写这一辅音字母,再加-ing.例如：run-running,swim-swimming等.2、以-al,-er,-ill结尾的动词,即使重音不在最后一个音节上,也要双写,再加-ing 如：travelling等.可以加动词ing的①及物动词.She likes drawing very much.；②某些短语动词.Mary is thinking of going back to New York.；③ do+限定词（my,some,any,the等）+ -ing,表示“做…事”之意,如：We often do our cleaning on Saturday afternoon.Will you do any shopping on Saturday this afternoon?④介词：Her sister is good at learning physics.；⑤形容词worth,busy等：This book is well worth reading.–ing作宾语带有宾语补足语时,要用it作为形式宾语,而将作宾语的-ing后置,如：We found it no good talking like that.Do you think it necessary trying again?