Change Past Perfect Active into Past Perfect Passive. 1. I had written the letter when he...

Question

Change Past Perfect Active into Past Perfect Passive.
1. I had written the letter when he came.
2. He had finished the work by 5 o’clock.
3. They had fulfilled the plan by the end of the last year.
4. People had made the first gas stove before the first electric stove appeared.
5. Doug Engelhart had earned nearly two dozen patens before he introduced the computer mouse.

Answer 1

1) the letter had been written by me when he came 
2)the work had been finished by 5 o'clock 
3) the plan had been fulfilled by them by the end of the last year 
4)the gas stove had been made by people before electric stove appeared 
5)two dozen patents had been earned by doug engelhart before he introduced the comp mouse