be动词例句：
The man is a science teacher.
这个男子是一位科学教师。
Mary's new dresses are colourful.
玛丽的新衣服色彩鲜艳。
I have been there before.
我以前去过那里。
My mother is in the kitchen now.
我妈妈现在在厨房里。
这四个都是陈述句，可以变成疑问句，方法简单，把主语和“be”或助动词对换位置即可：
Is the man a science teacher?
Are Mary's new dresses colourful?
Have I been there before?
Is mother in the kitchen now?