①这套纪念币是由国家发行、强制使用的

②这套纪念币的面额和发行量是由国家规定的

③这套纪念币能够执行贮藏手段和流通手段的职能

④这套纪念币在本质上是商品

将下列对话排序。

A. Do you have any black shirts?

B. Size 48. How much is it? 

C. That's too expensive for me.

D. Yes, I want a brown shirt.

E. Sorry, we don't have any brown shirts.

F. Can I help you? 

G. They're 85 yuan.

H. Yes, we do. What size do you want?

 F  D ____ ____ ____ ____ ____ ____ 

导致酸雨的主要原因是（　　）

⊙O为△ABC的内切圆，⊙O与AB相切于D，△ABC周长为12，BC=4，则AD=____