How must the seats in the cargo body of a truck used for transporting passengers be secured?

1. 1Not less than 0.3 m from the upper edge of the side board and 0.3-0.5 m from the floor, and seats located along the rear or side board must have sturdy backrests.
2. 2Not less than 0.4 m from the upper edge of the side board and 0.2-0.5 m from the floor, and seats located along the rear or side board must have sturdy backrests.
3. 3Not less than 0.3 m from the upper edge of the side board and 0.4-0.7 m from the floor, and seats located along the rear or side board must have sturdy backrests.
4. 4Not less than 0.2 m from the upper edge of the side board and 0.35-0.6 m from the floor, and seats located along the rear or side board must have sturdy backrests.