I'm pretty sure the answer is b
It would be much better if you've provided additional information, as it's not clear what your question is about. Anyway, I've found this question with options.
And the answer is Without exception, you must always stop when <span> A traffic officer instructs you to stop</span>.
The correct answer is PSC motor.
If you need more help, you can check on quizlet, I learnt about ecd from there lol