英语语法一个句子中，主语是三单，那在什么情况下动词

主语是三单，在一般现在时中动词跟随变为三单形式，词尾加-s或者-es。
He
often
goes
to
the
park
with
his
father.
Mary
never
washes
her
hands
in
cold
water.