How can you check the blind spots if the side rearview mirrors show only narrow angles of view?

• Asking the person sitting behind you
• Doing a shoulder check by turning your head
  Explanation:

  "Your side rearview mirrors show only narrow angles of view. You must turn your head to do shoulder checks to make sure there is nothing in your blind spots."
• Moving the head out of the window to check the blind spots
• There is no way, you have to take the risk