Proper use of the helmet means that the chin strap...
A)must not be fastened.
B)may be worn unfastened on urban roads.
C)must be worn correctly fastened, so that the helmet effectively performs its function.Correct
# Explanation: Correct Use of the Helmet Strap
The chin strap must be **properly fastened at all times** to ensure the helmet remains firmly on the head during an impact or accident. Without the strap fastened, the helmet can easily come off, completely losing its protective capacity. This safety measure is mandatory both on urban and interurban roads, with no exceptions.