语法填空题I asked my uncle, who plays ____1_____ piano well, ____

语法填空题
I asked my uncle, who plays ____1_____ piano well, _____2____ he would assess (评定) the tone of a second hand piano I was hoping to buy. We arrived _____3____ the house and Uncle Frank looked the piano over, then _____4____ (sit) down and played a mixture of honky-tonk numbers and classical pieces. When he finished, we told the family that we would call _____5_____ in 15 minutes.
Outside, Uncle Frank said that ______6_____ the wood was battered (坏掉的),the sound was good and we should buy it.
When I phoned the woman back, she sounded as if she was crying. ______7____ (concern), I asked, “What’s the matter?”
“We didn’t know the piano _____8______ play like that,” she replied. The piano wasn’t _____9_____ sale, and her daughter had to resume(重新开始) taking piano _____10_____.
第八个空填的是should 或could, 为什么不是用原型呢?前面不是有助动词didn't 吗?
第七个空格填的是concerned,为什么不是用它的副词形式呢？请解释。急啊！