Пассивный залог. Помогите

Проверьте пожалуйста предложения. Нужно сделать из активного пассивный залог.
The prime-minister made a speech to the nation. - A speech to the nation was made by the prime-minister.
The police arrested the car thief. - The car thief was arrested by the police.
The failure causes a depression. - A depression is caused by the failure.
We will inform our patron about this decision. - this decision will be informed our patron by us.
They think out a new plan. - A new plan is thought out by them.