a clock weight的用法和样例：
- A clock and two vases stood on the mantelpiece.
- Excuse me. This is a clock I buy in your store three day ago.
- The silence was succeeded by the striking of a clock.
- If you work in a factory, you usually have to punch a clock.
- A clock must above all be exact.
- A clock and two vases stood on the mantelpiece .