什么时候用rain 什么时候用rainy 什么时候又用raining

rianing是现在进行时，rainy是形容词，rian是动词

rain-指雨
rainy指雨天
raining-指正在下雨
分别是n adj verb
什么时候能用
比如说
today there will be rain
今天会下雨(用的主词)
This is a rainy day
今天是个雨天(用的是介绍词语)
there are raining in shanghai
上海现在在下雨(用的动词)
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如果我这样说你还不明白,我就无奈了

rain 可作动词也可做名词
－动词：It will rain today.今天会下雨
—名字：The rain is smaller now.现在雨下小了.
raining是rain作为动词的进行时态
It is raining heavily outside.现在外面雨很大.
rainy是形容词
It is a rainy day.今天是个雨天
估计初中的填空选择会这样出题：
I can go swimming with you tomorrow because the weather report said it will _____.（这里填rain,为动词）
I can go swimming with you tomorrow because the weather report said it will be a ____ day.(这里填rainy.为形容词)
I can go swimming with you today because it is _____ outside.(这里填raining,动词进行时态)

today is rainy - adj 今天是雨天
today rains - v 今天下雨
raining 意思相同，= today is a rainnig/rainy day,
today is raining 则为正在下雨