do既可以作助动词，又可以作实意动词，还可以放在动词前面用来强调。
do
you
have
any
money?中do是助动词；
he
is
doing
his
homework中do是动词。
i
do
love
her中do是用来强调“我是真的爱她”。
单数名词做主语或宾语谓语动词用is
例：monica
is
ross's
sister.
复数名词作主语或者是you作主语则用are
例：are
you
still
mad
at
me
and
rachel?
they
are
upset
because
they
lost
the
game.
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