陈述句什么时候加助动词
问题描述：
陈述句什么时候加助动词
答
陈述句中,强调谓语动词时,在谓语动词前加助动词,助动词的形式是原来谓语动词的形式,原谓语动词变为原形.例：
They bought some books yesterday.变成 They did buy some books yesterday.