Of the three potential answers, I have found an operator which does not throw an error, however it is not labelled as the correct answer.
I tried to get either the ping command or my injected command to execute using the stated answer, however despite trying the “correct” operator both in the middle and at the beginning, along with both URL and non-URL-encoded variants, and even trying with ‘+’ between the arguments and without, I could not get anything other than “Invalid Input” for the stated correct operator.
Unless I am missing something, it would appear that the “correct” answer is mislabeled as such.