a mug of cocoa的用法和样例：
- He has a mug of cocoa before bed.
- I have a mug of cocoa every morning.
- He likes to have a mug of cocoa before bed (= before going to bed).
- He made a mug of cocoa for me.
- He asked me to make him a mug of coffee.
- A mug of hot chocolate was just what she needed.