cut-cutting
sit-sitting
swim-swimming
permit-permitting
stop-stopping
drop-dropping
perfect-perferring
dig-digging
win-winning
run-running
put-putting
begin-beginning
get-getting
plan-planning
admit-admitting
规律：重读闭音节结尾 ,以辅音字母加一个元音字母结尾 ,双写这个辅音字母 ,再加ing