What do white motorway studs signify?

Answer: A — Lane markings

White motorway studs are used to mark lane boundaries on the road. The incorrect options are B, C, and D because they don't accurately describe the purpose of white motorway studs. B is incorrect because the edge of the road is usually marked by a solid white line, not motorway studs. C is incorrect because the space between carriageways is usually marked by a dashed white line or a solid barrier, not motorway studs. D is incorrect because a sliproad is typically marked by a solid white line, not motorway studs.