a mug of milk的用法和样例：
- He was so thirsty that he drank a mug of milk.
- I have a mug of milk and some bread for my breakfast.
- He has a mug of cocoa before bed.
- He asked me to make him a mug of coffee.
- A mug of hot chocolate was just what she needed.
- I have a mug of cocoa every morning.