论述音色的统一。
参考答案：
⑴钢琴音色统一的含义。⑵音色的成因。⑶张弦系统对音色的影响。⑷键盘、击弦机机械对音色的影响。⑸音色统一的必要调整。
国民经济
"What's this? "
_____. "[ ]
A. It's pen
B. This is pen
C. It's a pen
D. This is an pen
