论述乐音的性质。
参考答案：
⑴音高定义及其与振动频率的关系。⑵音量定义及其与振动幅度的关系。⑶音色定义及其与振动成分及相对强度的关系。⑷乐音的过渡性质。
根据图片填空完成句子。
1. ______________ do you see? I ______________ some children crying.
2. Jenny puts a new ______________ in her ______________ .
3. Here is a ______________ for your arm.
China is developing _______ of all the countries in the world. [ ]
A. fast
B. faster
C. fastest
D. the most fast
in her ______________ 
.
for your arm.