change from past perfect active into past perfeeect passive.
I couldnt geet into the hourse as I had lost the key. The key had been lost.
By the time my mom ceme I had cleaned my room. My room....
By 7 oclock I had done my morning exercises. Morning exercises....
Before we went out the teacher had checked our test. Our tests....
He was happy that he had found his watch. His wach....

Ответ:

My room had been cleaned by the time my mum came.  

My morning exercises had been done by 7 o'clock.  

Our tests had been checked by our teacher before we went  out.

His watch had been found by him.