1. A letter is written by Bruce every week.

2. The broken bike was mended by Li Lei this morning.

3. Two novels have been written by him so far.

4. Ten trees will be planted by them tomorrow.

5. A letter is being written by Lucy now.

6. The door must be locked when you leave.

7. The cake was made by me.

8. The house was built by the workers.

这些句子展示了被动语态的基本结构和用法，强调了动作的承受者而不是执行者。希望这些例子能帮助你更好地理解和运用被动语态。