问个英语句型转换
I have been skating for two hours.（改为一般疑问句）
____ you _____ _____ for two hours?
He has been working since an hours ago（改为否定句）
He ___ ___ ____ since an hour ago
He started playing the piano (six years ago)（对括号的部分提问）
_____ _____ he _____ playing the piano?