铅笔盒里有几支铅笔的英文为什么要加there啊?

这里是There be句型
There be表示 “存在有”,即当我们告诉某人某事存在(或不存在)常用这种结构.
例子：There is a book on the desk.课桌上有一本书.
How many people are there in the city?这个城市里有多少人口.
There is a pen and two books on the desk.课桌上有一个钢笔和两本书.
There are two books and a pen on the desk. 课桌上有两本书和一个钢笔.
There are some students and a teacher in the classroom. 在教室里有一些学生和一位老师.
There is a teacher and some students in the classroom. 在教室里有一位老师和一些学生.

How many pencils are there in the pencil-box？
这是 there be 句型的特殊疑问句 ，所以保留了there

There are a few pencils in the pencil case.
There- 那里

这是固定句型 There be 结构 意思为某地有某物。