In London the cars go . . . . . . . . the left side.

The question asks about the preposition that correctly describes the position of cars in London.

Think about how cars are positioned on a road.

'In' means inside something. Cars aren't inside the left side of the road.

'On' means something is on the surface of something else. This works well here. Cars drive *on* the road.

'To' means movement towards a place. This doesn't describe the position of the cars.

'Near' means close to something. This doesn't describe the exact position of the cars on the road.

Therefore, the correct preposition is 'on' because the cars drive on the left side of the road in London.