在两个情况下动词原型第三人单数变 es 或 ies ：
(1) 如果动词以单一个o 结尾：加 es
do => does
go => goes
veto => vetoes
但
boo => boos
ballyhoo => ballyhoos
(2) 如果动词以 y 结尾并y 前面有辅音：改 y 为 ies
copy => copies
deny => denies
fly => flies
try => tries
但
buy => buys
enjoy => enjoys
pay => pays