有关区域发展转型阶段的叙述，正确的是（  ）

这音大体可分为乐音与噪音：振动起来是有规律的、单纯的，是乐音；①____。种分类强调的不仅仅是音的客观物理属性，②____。举个简单例子：中午我在睡觉，邻居家的小孩就开始大声弹钢琴。钢琴曲很动听，对他而言是乐音。但是，动听的钢琴曲打扰了我，让我困倦，厌恶，所以对我而言就是噪音。可见，③____，在同一时间、同一地点会因不同的人而发生改变。

阅读下列对话, 根据首字母提示用适当的单词完成句子, 使对话完整、通顺。

W: Were you busy last weekend, Steven?

M: Yes. I was writing a book ①. a____ a kind of animal. How about you, Susan?

W: Me ②. t____ . I looked after my daughter. She was riding home ③. w____  it rained last Tuesday. ③. S____ she had a bad cold.  

M: I am ⑤ s____ to hear that. ⑥. H____ is your daughter now?

W: She is ⑦. f____ much better right now and is reading at home.

M: That ⑧. s____ good. Oh, I have ⑨. g____ a wonderful CD. It’s Titanic(泰坦尼克号). Very exciting.  

W: I know it. It’s a famous⑩. m____ .

M: Please take it to your daughter. I know she loves reading. I think she will love it.

W: Thanks so much, Steven.

M: You are welcome.

设二次函数y=ax²+bx+c（a＞0）的图象与x轴的两个交点A（x₁，0），B（x₂，0），抛物线的顶点为C，显然△ABC为等腰三角形．