sometimes it rains 为什么填rains而不填rain?

sometimes it rains 为什么填rains而不填rain? It+often+rains++summer为什么填in It never rains here in spring,()?反义疑问句填does it为什么不填is it It rains sometimes可以说It is sometimes rain it rains sometimes When it rains,she ____ a bus to work.怎么填?A.rain B.is raining Look at the rain,it rains ______（heavy）填什么? It was always______there.空格中填rain还是rainy还是 rains? sometimes it rains和it rains sometimes 是不是一样的? You can't leave now. It (rain) outside.怎么填啊,说一下什么时候填rains、ri but it rains sometimes 为什么没有系动词 为什么“if it rains”后的“rain”很多答案上说要加‘s’,而很多有说是“if it will rain”到