The first and the last two of those answers are valid Python code, and they should all print Hello World and thus all be accepted. The second and third answers are not valid Python code and will give syntax errors when run.
As the name indicates, CodeRunner is intended to run code as part of the marking process and it can't run invalid code.
You could modify the prototype to convert all Python keywords and built-in library functions to lower-case but this seems like the wrong solution. Why not teach your students to write valid Python code?