keep的用法是什么.语法内容

to
keep
动词不定式
it's
a
constant
struggle
to
try
to
keep
them
up
to
par.
要让他们达标，需要不断努力。
i
managed
to
keep
my
parents
in
the
dark
about
this.
我设法对父母瞒下了此事。