It is a blank web page.
So get the help from the hint:
X老师上课讲了Robots协议，小宁同学却上课打了瞌睡，赶紧来教教小宁Robots协议是什么吧。
Robots Protocal is uesd to constrain the range when someone automatically attains information(such as web page source code) with web crawler, and generally stored under root directory.
So...you know how to exploit this protocal.
The hint is obvious.