分四种情况：
1、直接在动词后加--ing：
buying calling enjoyingtelling waiting working sleeping washing dressing starting seeing cleaning cooking learning sweeping happening helping painting meaning wanting being
2、去e加--ing（以不发音的e结尾的):
driving takingleaving lovng decorating giving
3、双写最后一个字母加ing（以重读闭音节结尾并且末尾只有一个辅音字母的）
puttingshoppingcutting
4、把ie去掉变成y再加ing:lie-lying
