In a passenger car, a telephone conversation using a hands-free system without hand operation or earphones...

Correct answer

is permitted, but it should be understood that it may also cause distractions.

Is permitted under those conditions but can cause cognitive distraction, delay reactions or cause important information to be missed. Article 18 requires constant attention: the exception does not permit handling the phone or wearing earphones for the call. No conversation duration guarantees safety. Avoid attending to it when distracting and stop somewhere permitted and safe to do so.