Read and choose. （读一读，选择答语）
1. — Good afternoon!
— [ ]
A. Good morning!
B. Good afternoon!
C. Goodbye!
2. — What's your name?
— [ ]
A. I'm from China.
B. I'm Lingling.
C. Nice to meet you.
3. — Where are you from?
— [ ]
A. I'm from America.
B. I'm John.
C. Good morning!
4. — Nice to meet you !
— [ ]
A. I'm from China.
B. I'm Li Ming.
C. Nice to meet you, too.
5. — Hello ! Boys and girls. I'm Mrs Lin.
— [ ]
A. Goodbye! Mrs Lin.
B. Hello ! Mrs Lin.
C. Thank you, Mrs Lin.
分别通过半径为
的凸形路面
与凹形路面
时两路面所受的压力之比为
∶
=________。