Here's a problem to solve: Robots can perform tasks that are dangerous for humans. What is the MAJOR limitation to the use of robots?

Among the 4 following options, which is the correct answer?

- A: The assembly pieces must be very small.
 
- B: The assembly process must remain exactly the same.
 
- C: Robots require regular maintenance.
 
- D: Robots must be provided with electricity.
 