Final answer:
The minimum height requirement for a toe board above the surface of the work area is 140mm, which helps ensure safety by preventing objects from falling off the edge of the work platform.
Step-by-step explanation:
A toe board on a work platform is a safety feature designed to prevent tools and other objects from falling off and causing injury or damage. When you ask, "A toe board must not be less than," you are inquiring about the minimum height requirement stipulated for toe boards to provide adequate safety. The correct answer to the question is: B) 140mm in height above the surface of the work area. This is the minimum height requirement that ensures objects cannot easily slip off the edge.