rainy是形容词，“多雨的；下雨的”；rain是
不可数名词，“雨水”；rains可指“几场雨,大阵雨”，the
rains指“雨季”；raining是形容词，“下雨的”。例如：
Soon
the
rainy
season
sets
in.
很快雨季到了。
It
looks
like
rain.
天要下雨。(此处的rain是不可数名词)
The
rains
that
year
were
good,
they
were
coming
nicely
just
as
the
crops
needed
them.
那一年的雨季真没说的,正当庄稼需要水的时候就下雨了。
We
have
to
play
inside
because
it
is
raining.
因为天下雨，我们不得不在屋里玩。