Final answer:
A diamond-shaped road sign indicates a warning such as 'Slippery when wet' and alerts drivers to potential hazards or changes in driving conditions.
Step-by-step explanation:
A diamond-shaped road sign typically indicates a warning or caution on the road. It warns drivers about a potential hazard or a change in the driving conditions ahead. The correct message indicated by a diamond-shaped road sign among the options given is B) Slippery when wet. This is a common warning sign that alerts drivers to reduce speed and take extra care since the road may be more slippery than usual, especially after rain. It does not denote 'No right turn' or 'School crossing', which are usually indicated by other types of signs.