What must you legally make sure are in good condition?

Answer: A — Windscreen, headlights, seatbelts

You legally must make sure that your vehicle's windscreen, headlights, and seatbelts are in good condition. Although the other options listed may also be important for the overall functionality of your vehicle, they are not specifically mentioned as legal requirements. Additionally, the condition of the windscreen, headlights, and seatbelts directly impact your safety while driving, making them the top priority for being in good condition.