各位大侠，请看下面一道语法题：

Because geophysics embraces the concepts, data, and methods of variety other sciences, it

is very board in scope, and its boundaries are hard to define.

在这里 variety other 应该改为 various other 或 a variety of other。但最后一个是不是也该改为

to be defined? 多谢指教。

its boundaries are hard to define意思是边界是很难定义的。

如果我们要说一本书很难读懂就会说"hard to read"or"hard to understand"绝对不会说"hard to be read"

这样说能明白吗？