1.Snow covered the mountains.
The mountains were covered by snow .
2.They develop an environmentally friendly type of washing powder.
An environmental friendly type of washing powder is developed by them.
3.My teachers check the copybooks every day.
The copybooks are checked by my teachers everyday.
4.The lady gave me the keys.
The keys were given me by the lady.
5.The professor will show the students an old bone.
An old bone will be shown to the students by the professor.
6.Who said it?
By whom was it said?
7.People said that the President is ill.
It was said that the president is ill.
8.We will eat the dinner later.
The dinner will be eaten by us later.
9.Where do you write letters?
Where are the letters written?
10.My Dad fixed his equipment yesterday.
My Dad's equipment was fixed by him yesterday.