What must you do when transporting bicycles on the roof of your car?

You answered correctly. When transporting bicycles on the roof of your car, all three points are important. First, the holding device and bicycles must be securely fastened to prevent them from falling off while driving. Second, you should avoid driving at high speeds because the added weight and air resistance can affect the stability of your car and the safety of the load. Third, it's necessary to regularly check the fixing devices during your trip, as vibrations or movements can loosen the attachments. Always follow these steps for safe bicycle transport on the roof.