a portion of roast beef的用法和样例：
- Good! I'm so starving that I can eat a horse. I'm going to have at least five portions of roast beef and lamb.
- A portion of profits or earnings; a share.
- The driver must bear a portion of the blame for the accident.
- Pearl carved up the roast beef and gave us each a portion.
- A "block" is a portion of a plantation.