feel的过去式是felt,fall的过去式是fell,两种变化的规律是什么?

feel的变化和以下单词差不多：
sleep(slept)
keep(kept)
sweep(swept)
fall的变化（改动一个字母）和下面的单词差不多：
sit sat
babysit babysat
come came
become became
draw drew
drink drank
drive drove
get got
forget forgot
give gave
grow grew
know knew
make made
ride rode
ring rang
run ran
send sent
sing sang
spend spent
swim swam
win won
write wrote
常用的就这些,主要的就是背

feel的过去式变el为lt fall的过去式变a为e