编辑一篇文章，将其中的被动语态改为主动语态。
这是一篇短文，包含多个被动语态的句子。
下面是原文和改为主动语态后的文章：

原文： 

1. The cake was baked by Sarah.
2. The book was written by J.K. Rowling.
3. The window was broken by the ball.
4. The car was built by a team of engineers.
5. The letter was sent by the postman.

改为主动语态后的文章：

1. Sarah baked the cake.
2. J.K. Rowling wrote the book.
3. The ball broke the window.
4. A team of engineers built the car.
5. The postman sent the letter.