Etresoft, thank you very much for your reply. I can open any other sites except "adobe.com". I am pretty sure that XAMPP caused this problem. The whole story likes this:
1. I installed XAMPP, started Apache;
2. Then I typed "localhost" in Safari, I got this page:
3. then I click "Flash Art" on the left panel, I got the following page:
4. I clicked "Missing Plug-in" in the middle of the page, then I got:
5. After I clicked "Okay", I got the following page:
6. I noticed the website address was "http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash", and it couldn't be opened.
So I tried to open "www.adobe.com" in Safari, then surprisingly, the address automatically changed to "http://www.adobe.com/xampp/", see the following picture:
7. Then I tried to open other adobe websites, and found out that as long as the addresses begins with "www.adobe.com/~~~~~~", they could not be opened.
And XAMPP directs the address "adobe.com" to "localhost" page. In other words, there is no difference when you type "adobe.com" or "localhost" in Safari.
8. When I turn off XAMPP, Safari tell me that it couldn't connect to the server, clearly, when you turn off XAMPP, you turn off "localhost" page. And "adobe.com" points to "localhost", so Safari said "it couldn't connect to the server".
Reset Safari, delete "XAMPP", restart computer, all didn't solve the problem. I am very frustrated. I posted all details, because this is my first time to use "XAMPP", and wish the problem can be solved soon.
Thank you all very much!!