c天正在下雨。 The sky is raining It is raining. (While mentioning the weather conditions, native speakers of English tend to begin with the pronoun"it",e.g. It is rather windy today. c.天正在下雨。  *The sky is raining.  It is raining.  (While mentioning the weather conditions, native speakers of English tend to begin with the pronoun “it”, e.g. It is rather windy today.)