To work with Screen Design Aid (SDA) in IBM i (formerly known as AS/400), the command to use is:
C. STRSDA
The command "STRSDA" is used to start the Screen Design Aid utility. SDA is a tool that allows you to create, modify, and maintain screens and display files on the IBM i system.
Option A, "WRKSDA," is not a valid command. There is no built-in command named "WRKSDA" in IBM i.
Option B, "CHGSDA," is not a valid command. There is no built-in command named "CHGSDA" in IBM i.
Option D, "UPDSDA," is not a valid command. There is no built-in command named "UPDSDA" in IBM i.
Therefore, the correct answer is C. STRSDA.