a catty comment的用法和样例：
- How much is it? -Twenty cents a catty.
- These eggplants are really good. Only $30 a catty.
- My son sold to a little teacher younger brother by 30 pieces of a catty price.
- A catty remark.
- Now, his wife developed a strict menu: Breakfast: 2 cucumbers, half a catty of milk, 2 eggs.