"It's raining" 是表示 "下雨天" 的常用说法。
来源："It's raining" 是英语中表示下雨天的常用句型，其中 "it" 是形式主语，"is" 是助动词，"raining" 是现在分词，组成了一个现在进行时的句子。
例句及翻译:
"It's raining outside, you should bring an umbrella." (外面在下雨，你应该带把伞)
"I don't pke to go out when it's raining." (我不喜欢在下雨天出门)
"It's been raining all day, I'm so sick of it." (一整天都在下雨，我太厌倦了)