Active and Passive Voice

How do people learn languages?
How are languages learned?

Somebody cleans the room every day.
The room is cleaned every day.

They cancelled all flights because of the fog.
All flight were cancelled because of the fog.

People didn't use this road very often.
This road wasn't used very often.

Somebody accused me of stealing money.
I was accused of stealing money.

People advised us not to go out alone.
We were advised not to go out alone.

How do people make a cheese cake?
How is a cheese cake made?

You must go over the exercise before you hand in.
The exercise must be go over before you hand in.