What's the purpose of green-and-yellow fluorescent studs on a motorway? What's the purpose of green-and-yellow fluorescent studs on a motorway?

• Possible answers:

   
• A. They mark the lanes in a contraflow system
• B. They separate the slip road from the motorway
• C. They mark access points for emergency services
• D. They separate the edge of the hard shoulder from the grass verge