Most Difficult CAPTCHA

I hate websites use CAPTCHA, but we know some websites use it to against internet robots. A popular online file host site Rapidshare use CAPTCHA. Do you know what is most difficult CAPTCHA? How can you answer it? Check out this picture below.




我不喜欢CAPTCHA，但我知道有不少网站使用它来防止网络机器人。流行的网络文件储存网站Rapidshare就使用CAPTCHA。你知道最难得CAPTCHA是什么？你能回答出来吗？看一下上面的图片。